perilous (adj.) Look up perilous at Dictionary.com
c. 1300, from Old French perillos "perilous, dangerous" (Modern French périlleux) "dangerous, hazardous," from Latin periculosus "dangerous, hazardous," from periculum "a danger, attempt, risk" (see peril). Related: Perilously; perilousness.
perimeter (n.) Look up perimeter at Dictionary.com
early 15c., "line around a figure or surface," from Latin perimetros, from Greek perimetron "circumference," from peri- "around" (see peri-) + metron "measure" (see meter (n.2)). Military sense of "boundary of a defended position" is attested from 1943.
perinatal (adj.) Look up perinatal at Dictionary.com
1952, from peri- + natal.
perineum (n.) Look up perineum at Dictionary.com
"region of the body between the anus and the genital organs" (jocularly called a taint), early 15c., from Medieval Latin perinaeon, Late Latin perineum, from Greek perinaion, perinaios, from peri- "near" (see peri-) + inan "to carry off by evacuation," of unknown origin.
period (n.) Look up period at Dictionary.com
early 15c., "course or extent of time," from Middle French periode (14c.) and directly from Medieval Latin periodus "recurring portion, cycle," from Latin periodus "a complete sentence," also "cycle of the Greek games," from Greek periodos "cycle, circuit, period of time," literally "a going around," from peri- "around" (see peri-) + hodos "a going, travelling, journey; a way, path, road," from PIE root *ked- "to go, yield" (see cede).

Sense of "repeated cycle of events" led to that of "interval of time." Meaning "dot marking end of a sentence" first recorded c. 1600, from similar use in Medieval Latin (in late 16c. English it meant "full pause at the end of a sentence"). Sense of "menstruation" dates from 1822. Educational sense of "portion of time set apart for a lesson" is from 1876. Sporting sense attested from 1898. As an adjective from 1905; period piece attested from 1911.
periodic (adj.) Look up periodic at Dictionary.com
1640s, from French périodique (14c.), from Latin periodicus, from periodus (see period).

Periodic table in chemistry (1889) is from notion of the arrangement, in which similar properties recur at intervals in elements in the same area as you read down the rows of the table. This sense of the word is attested from 1872 (periodic law).
periodical (adj.) Look up periodical at Dictionary.com
c. 1600, from periodic + -al (1). As a noun meaning "magazine published at regular intervals," attested from 1798. Related: Periodically.
periodicity (n.) Look up periodicity at Dictionary.com
1805, from French périodicité (1796), from périodique, from Latin periodicus (see periodic).
periodontal (adj.) Look up periodontal at Dictionary.com
1848, literally "around the tooth," from peri- + Greek odon (genitive odontos) "tooth" (see tooth).
periodontics (n.) Look up periodontics at Dictionary.com
1948, from periodontia (1914; see periodontal) + -ics. Periodontic (adj.) is attested by 1889.
periodontist (n.) Look up periodontist at Dictionary.com
1913; see periodontal + -ist.
periodontitis (n.) Look up periodontitis at Dictionary.com
1842; see periodontal + -itis "inflammation."
periodontium (n.) Look up periodontium at Dictionary.com
1828; see periodontal.
periorbital (adj.) Look up periorbital at Dictionary.com
1838, from medical Latin periorbita, a hybrid from Greek peri (see peri-) + Latin orbita (see orbit).
periosteum (n.) Look up periosteum at Dictionary.com
1590s, from Modern Latin periosteum, Late Latin periosteon, from Greek periosteon, neuter of periosteos "round the bones," from peri- (see peri-) + osteon (see osseous).
peripatetic (n.) Look up peripatetic at Dictionary.com
c. 1400, "disciple of Aristotle," from Old French perypatetique (14c.), from Latin peripateticus "pertaining to the disciples or philosophy of Aristotle," from Greek peripatetikos "given to walking about" (especially while teaching), from peripatein "walk up and down, walk about," from peri- "around" (see peri-) + patein "to walk, tread" (see find (v.)). Aristotle's custom was to teach while strolling through the Lyceum in Athens. In English, the philosophical meaning is older than that of "person who wanders about" (1610s).
peripatetic (adj.) Look up peripatetic at Dictionary.com
1560s in the philosophical sense, 1640s in the literal sense; see peripatetic (n.).
peripeteia (n.) Look up peripeteia at Dictionary.com
also peripetia, 1590s, from Greek peripeteia "a turn right about; a sudden change" (of fortune, in a tragedy), from peri- "around" (see peri-) + stem of piptein "to fall" (see symptom).
peripheral (adj.) Look up peripheral at Dictionary.com
1803, from periphery + -al (1). An earlier formation was peripherial (1670s). Related: Peripherally. As a noun, peripherals, "peripheral devices of a computer," is from 1966.
periphery (n.) Look up periphery at Dictionary.com
late 14c., "atmosphere around the earth," from Old French periferie (Modern French périphérie), from Medieval Latin periferia, from Late Latin peripheria, from Greek peripheria "circumference, outer surface, line round a circular body," literally "a carrying around," from peripheres "rounded, moving round, revolving," peripherein "carry or move round," from peri- "round about" (see peri-) + pherein "to carry" (see infer). Meaning "outside boundary of a surface" attested in English from 1570s; general sense of "boundary" is from 1660s.
periphrasis (n.) Look up periphrasis at Dictionary.com
1530s, from Latin periphrasis "circumlocution," from Greek periphrasis, from periphrazein "speak in a roundabout way," from peri- "round about" (see peri-) + phrazein "to express" (see phrase (n.)).
periphrastic (adj.) Look up periphrastic at Dictionary.com
1805, from French périphrastique and directly from Greek periphrastikos, from periphrazein (see periphrasis). Related: Periphrastical (1630s).
periscope (n.) Look up periscope at Dictionary.com
viewing apparatus on a submarine, 1899, formed in English from peri- "around" + -scope "instrument for viewing." Earlier (1865) a technical term in photography. Related: Periscopic.
perish (v.) Look up perish at Dictionary.com
mid-13c., from periss- present participle stem of Old French perir "perish, be lost, be shipwrecked" (12c.), from Latin perire "to be lost, perish," literally "to go through," from per- "through, completely, to destruction" (see per) + ire "to go" (see ion). Related: Perished; perishing.
perishable (adj.) Look up perishable at Dictionary.com
late 15c., perysabyl, from Middle French périssable, and later (in modern form), 1610s, directly from perish + -able. As a noun, perishables, in reference to foodstuffs, is attested from 1895.
peristalsis (n.) Look up peristalsis at Dictionary.com
1859, Modern Latin peristalsis; see peristaltic.
peristaltic (adj.) Look up peristaltic at Dictionary.com
1650s, from Modern Latin, from Greek peristaltikos (Galen), literally "contracting around," from peri (see peri-) "around, about" + stalsis "checking, constriction," related to stellein "draw in, bring together; set in order" (see diastole).
peristyle (n.) Look up peristyle at Dictionary.com
1610s, from French péristyle "row of columns surrounding a building" (mid-16c.), from Latin peristylum, from Greek peristylon "colonnade around a temple or court," noun use of neuter of peristylos "surrounded with a colonnade," from peri- "around" (see peri-) + stylos "pillar," from PIE root *stā- "to stand, set down, make or be firm" (see stet).
peritoneum (n.) Look up peritoneum at Dictionary.com
early 15c., from Late Latin peritonaeum, from Greek peritonaion "abdominal membrane," literally "part stretched over," noun use of neuter of peritonaios "stretched over," from peri- "around" (see peri-) + teinein "to stretch" (see tenet). Related: Peritoneal.
peritonitis (n.) Look up peritonitis at Dictionary.com
1776, medical Latin, coined c. 1750 by French pathologist François-Boissier de la Croix de Sauvages (1706-1767) from Greek peritonos (from peritonaion; see peritoneum) + -itis "inflammation."
periwig (n.) Look up periwig at Dictionary.com
1520s, perwyke, popular corruption of perruck, from Middle French perruque (see peruke).
periwinkle (n.1) Look up periwinkle at Dictionary.com
evergreen plant, c. 1500, diminutive of parvink (12c.), from Old English perwince, from Late Latin pervinca "periwinkle" (4c.), from Latin, perhaps from pervincire "to entwine, bind," from per- "thoroughly" (see per) + vincire "to bind, fetter" (see wind (v.1)).
periwinkle (n.2) Look up periwinkle at Dictionary.com
kind of sea snail, 1520s, apparently an alteration of Old English pinewincle (probably by influence of Middle English parvink; see periwinkle (n.1)); from Old English pine-, which probably is from Latin pina "mussel," from Greek pine. The second element is wincel "corner; spiral shell," from Proto-Germanic *winkil-, from PIE root *weng- "to bend, curve" (see wink (v.)).
perjure (v.) Look up perjure at Dictionary.com
mid-15c. "swear falsely" (implied in perjured; late 13c. in Anglo-French), from Old French parjurer "to break one's word, renege on a promise" (11c.), from Latin periurare "to swear falsely, break one's oath" (see perjury). Reflexive sense is from 18c.
perjury (n.) Look up perjury at Dictionary.com
late 14c., "act of swearing to a statement known to be false," via Anglo-French perjurie (late 13c.) and Old French parjurée "perjury, false witness," both from Latin periurium "a false oath," from periurare "swear falsely," from per- "away, entirely" (see per) + iurare "to swear" (see jury (n.)). Related: Perjurious.
perk (v.) Look up perk at Dictionary.com
late 14c., "to make oneself trim or smart," perhaps from Old North French perquer "to perch" (Modern French percher; see perch (n.1)), on notion of a bird preening its plumage. Sense of "raise oneself briskly" is first attested 1520s; perk up "recover liveliness" is from 1650s. Related: Perked; perking.
perk (n.) Look up perk at Dictionary.com
1869, shortened colloquial form of perquisite (q.v.), also perq. As a verb, 1934 as shortened and altered form of percolate, also perc.
perky (adj.) Look up perky at Dictionary.com
1820, from perk (v.) + -y (2). Of young women's breasts since at least 1937. Related: Perkily; perkiness.
perm (n.) Look up perm at Dictionary.com
1927, shortened form of permanent wave (1909). The verb is first recorded 1928.
permaculture (n.) Look up permaculture at Dictionary.com
by 1978, from permanent + agriculture or culture.
permafrost (n.) Look up permafrost at Dictionary.com
1943, coined in English by Russian-born U.S. geologist Siemon W. Muller (1900-1970) from perm(anent) frost.
permanence (n.) Look up permanence at Dictionary.com
early 15c., from Middle French permanence and directly from Medieval Latin permanentia (early 14c.), from Latin permanens (see permanent). Related: Permanency.
permanent (adj.) Look up permanent at Dictionary.com
early 15c., from Middle French permanent (14c.) or directly from Latin permanentem (nominative permanens) "remaining," present participle of permanere "endure, hold out, continue, stay to the end," from per- "through" (see per) + manere "stay" (see mansion). As a noun meaning "permanent wave," by 1909. Of clothing, permanent press attested from 1964.
permanently (adv.) Look up permanently at Dictionary.com
late 15c., from permanent + -ly (2).
permeability (n.) Look up permeability at Dictionary.com
1733, from permeable + -ity, or else from French perméabilité.
permeable (adj.) Look up permeable at Dictionary.com
early 15c., from Late Latin permeabilis "that can be passed through, passable," from Latin permeare "to pass through, go over," from per- "through" (see per) + meare "to pass," from PIE root *mei- (1) "to change" (see mutable). Related: Permeably.
permeant (adj.) Look up permeant at Dictionary.com
1640s, from Latin permeantem (nominative permeans), present participle of permeare "to pass through" (see permeable).
permeate (v.) Look up permeate at Dictionary.com
1650s, from Latin permeatus, past participle of permeare "to pass through" (see permeable). Related: Permeated; permeating.
permeation (n.) Look up permeation at Dictionary.com
1620s, noun of action from Latin permeare (see permeate).
Permian Look up Permian at Dictionary.com
1841, "pertaining to the uppermost strata of the Paleozoic era," named by British geologist Sir Roderick Impey Murchison (1792-1871) for the region of Perm in northwestern Russia, where rocks from this epoch are found.