pit (n.1)

Old English pytt (Kentish *pet), "natural or man-made depression in the ground, water hole, well; grave," from Proto-Germanic *putt- "pool, puddle" (source also of Old Frisian pet, Old Saxon putti, Old Norse pyttr, Middle Dutch putte, Dutch put, Old High German pfuzza, German Pfütze "pool, puddle"), an early borrowing from Latin puteus "well, pit, shaft."

The Latin word is perhaps from PIE root *pau- (2) "to cut, strike, stamp," but there are phonetic and sense objections.

Short u makes it impossible to directly derive puteus from paviō 'to strike'. It might be related to putāre 'to prune', but this is semantically less attractive, and the suffix -eus can then hardly be interpreted as indicating a material. Therefore, puteus may well be a loanword. [de Vaan]

Meaning "abode of evil spirits, hell" is attested from late 12c.  Meaning "very small depression or dent in the surface of an object" is from early 15c. The anatomical sense of "natural depression or hollow in some part of the body" is by late 13c,; the pit of the stomach (1650s) is so called from the slight depression there between the ribs; earlier words for it were breast-pit (late 14c.), heart-pit (c. 1300).

The meaning "part of a theater on the floor of the house, lower than the stage," is from 1640s; the sense of "that part of the floor of an exchange where business is carried on" is by 1903, American English. The pit dug under a large engine or other piece of machinery to allow workers to examine or repair it is attested by 1839; this later was extended in auto racing to "area at the side of a track where cars are serviced and repaired" (by 1912).

pit (n.2)

"hard seed," 1841, from Dutch pit "kernel, seed, marrow," from Middle Dutch pitte, ultimately from Proto-Germanic *pithan-, source of pith (q.v.).

pit (v.)

mid-15c., "to put or set in or into a pit," from pit (n.1); especially for purposes of fighting (of cocks, dogs, pugilists) from 18c. Hence the figurative sense of "to set in rivalry, match as opponents" (1754). Compare pit-bull as a dog breed, attested from 1922, short for pit-bull terrier (by 1912). The meaning "make pits in, form a little pit or hollow in" is from late 15c. Related: Pitted; pitting.

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Definitions of pit from WordNet
pit (n.)
a sizeable hole (usually in the ground);
they dug a pit to bury the body
Synonyms: cavity
pit (n.)
a concavity in a surface (especially an anatomical depression);
Synonyms: fossa
pit (n.)
the hard inner (usually woody) layer of the pericarp of some fruits (as peaches or plums or cherries or olives) that contains the seed;
Synonyms: stone / endocarp
pit (n.)
(Christianity) the abode of Satan and the forces of evil; where sinners suffer eternal punishment; "Hurl'd headlong...To bottomless perdition, there to dwell"- John Milton; "Hell is paved with good intentions"-Dr. Johnson;
a demon from the depths of the pit
Synonyms: Hell / perdition / Inferno / infernal region / nether region
pit (n.)
an enclosure in which animals are made to fight;
pit (n.)
(commodity exchange) the part of the floor of a commodity exchange where trading in a particular commodity is carried on;
pit (n.)
(auto racing) an area at the side of a racetrack where the race cars are serviced and refueled;
pit (n.)
a trap in the form of a concealed hole;
Synonyms: pitfall
pit (n.)
a surface excavation for extracting stone or slate;
a British term for `quarry' is `stone pit'
Synonyms: quarry / stone pit
pit (n.)
lowered area in front of a stage where an orchestra accompanies the performers;
Synonyms: orchestra pit
pit (n.)
a workplace consisting of a coal mine plus all the buildings and equipment connected with it;
Synonyms: colliery
pit (v.)
set into opposition or rivalry;
pit a chess player against the Russian champion
Synonyms: oppose / match / play off
pit (v.)
mark with a scar;
Synonyms: scar / mark / pock
pit (v.)
remove the pits from;
pit plums and cherries
Synonyms: stone