romance (n.) Look up romance at Dictionary.com
c.1300, "a story, written or recited, of the adventures of a knight, hero, etc.," often one designed principally for entertainment," from Old French romanz "verse narrative" (Modern French roman), originally an adverb, "in the vernacular language," from Vulgar Latin *romanice scribere "to write in a Romance language" (one developed from Latin instead of Frankish), from Latin Romanicus "of or in the Roman style," from Romanus "Roman" (see Roman).

The sense evolution is because medieval vernacular tales usually told chivalric adventures full of marvelous incidents and heroic deeds. In reference to literary works, often in Middle English meaning ones written in French but also applied to native compositions. Literary sense extended by 1660s to "a love story." Meaning "adventurous quality" first recorded 1801; that of "love affair" is from 1916. Romance novel attested from 1964. Compare Romance (adj.).
romance (v.) Look up romance at Dictionary.com
late 14c., "recite a narrative," from Old French romancier "narrate in French; translate into French," from romanz (see romance (n.)). Later "invent fictitious stories" (1670s), then "be romantically enthusiastic" (1849); meaning "court as a lover" is from 1938, probably from romance (n.). Related: Romanced; romancing.
Romance (adj.) Look up Romance at Dictionary.com
mid-14c., "French; in the vernacular language of France" (contrasted to Latin), from Old French romanz "French; vernacular," from Late Latin Romanice, from Latin Romanicus (see Roman). Extended 1610s to other modern tongues derived from Latin (Spanish, Italian, etc.); thus "pertaining to the languages which arose out of the Latin language of the provinces of Rome." Compare romance (n.).