pit (n.1) Look up pit at Dictionary.com
"hole, cavity," Old English pytt "water hole, well; pit, grave," from Proto-Germanic *puttjaz "pool, puddle" (cognates: Old Frisian pet, Old Saxon putti, Old Norse pyttr, Middle Dutch putte, Dutch put, Old High German pfuzza, German Pfütze "pool, puddle"), early borrowing from Latin puteus "well, pit, shaft." Meaning "abode of evil spirits, hell" is attested from early 13c. Pit of the stomach (1650s) is from the slight depression there between the ribs.
pit (v.) Look up pit at Dictionary.com
mid-15c., "to put into a pit," from pit (n.1); especially for purposes of fighting (of cocks, dogs, pugilists) from 1760. Figurative sense of "to set in rivalry" is from 1754. Meaning "to make pits in" is from late 15c. Related: Pitted; pitting. Compare Pit-bull as a dog breed attested from 1922, short for pit-bull terrier (by 1912). This also is the notion behind the meaning "the part of a theater on the floor of the house" (1640s).
pit (n.2) Look up pit at Dictionary.com
"hard seed," 1841, from Dutch pit "kernel, seed, marrow," from Middle Dutch pitte, ultimately from West Germanic *pithan-, source of pith (q.v.).