Etymology
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snake (n.)

Old English snaca, from Proto-Germanic *snakon (source also of Old Norse snakr "snake," Swedish snok, German Schnake "ring snake"), from PIE root *sneg- "to crawl, creeping thing" (source also of Old Irish snaighim "to creep," Lithuanian snakė "snail," Old High German snahhan "to creep"). In Modern English, gradually replacing serpent in popular use.

Traditionally applied to the British serpent, as distinguished from the poisonous adder. Meaning "treacherous person" first recorded 1580s (compare Old Church Slavonic gadu "reptile," gadinu "foul, hateful"). Applied from 17c. to various snake-like devices and appliances. Snakes! as an exclamation is from 1839.

Snake eyes in crap-shooting sense is from 1919. Snake-bitten "unlucky" is sports slang from 1957, from a literal sense, perhaps suggesting one doomed by being poisoned. The game of Snakes and Ladders is attested from 1907. Snake charmer is from 1813. Snake pit is from 1883, as a supposed primitive test of truth or courage; figurative sense is from 1941. Phrase snake in the grass is from Virgil's Latet anguis in herba [Ecl. III:93].

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snake (v.)

1650s, "to twist or wind (hair) into the form of a snake," from snake (n.). The intransitive sense of "to move like a snake" is attested from 1848; that of "to wind or twist like a snake" (of roads, etc.) is from 1875. Related: Snaked; snaking.

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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).

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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.).

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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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money-pit (n.)

"edifice or project requiring constant outlay of cash with little to show for it," 1986 (year of a movie of the same name); see money (n.) + pit (n.). Before that (1930s), it was used for the shaft on Oak Island, Nova Scotia, that supposedly leads to treasure buried by Capt. Kidd or some other pirate. "Whether that name refers to the treasure or the several million dollars spent trying to get the treasure out is unclear." [Popular Mechanics, Sept. 1976]

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ash-pit (n.)

"repository for ashes," especially "lower part of a furnace," 1797, from ash (n.1) + pit (n.1). Older is ash-hole (1640s).

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corn-snake (n.)

popular name of a type of large but harmless rat-snake of the southeastern and central U.S., often found in cornfields, 1670s, from corn (n.1) + snake (n.).

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milk-snake (n.)

"A handsome and harmless serpent" [Century Dictionary], one of the larger snakes of the U.S., common in many states, by 1812, from milk (n.) + snake (n.). Also called chicken-snake (attested by 1793), house-snake, and thunder-and-lightning snake.

It [the milk-snake] sometimes in this county has been known to enter a grist-mill and remain a length of time for the apparent purpose of feeding on the mice which were there attainable. It is probable this is one principal object of his frequenting dwelling houses, and not always for the purpose of obtaining milk, as is generally supposed. [The American Journal of Science and Arts, April 1844]
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pit-viper (n.)

venomous serpent, so called from the characteristic depression between the eyes and the nose, by 1872, from pit (n.1) + viper.

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