c. 1300, "limbless reptile," also the tempter in Genesis iii.1-5, from Old French serpent, sarpent "snake, serpent" (12c.), from Latin serpentem (nominative serpens) "snake; creeping thing," also the name of a constellation, from present participle of serpere "to creep."

This is reconstructed to be from PIE *serp- "to crawl, creep" (source also of Sanskrit sarpati "creeps," sarpah "serpent;" Greek herpein "to creep," herpeton "serpent;" Albanian garper "serpent").

Serpent and snake now mean precisely the same thing ; but the word serpent is somewhat more formal or technical than snake, so that it seldom applies to the limbless lizards, many of which are popularly mistaken for and called snakes, and snake had originally a specific meaning. [Century Dictionary, 1902]

Used figuratively of things spiral or regularly sinuous, such as a type of musical instrument with a twisting tube (1730). Serpent's tongue as figurative of venomous or stinging speech is from mistaken medieval notion that the serpent's tongue was its "sting." Serpent's tongue also was a name given to fossil shark's teeth (c. 1600). Serpent-charmer is by 1861.

Middle English naddre, from Old English (West Saxon) næddre (Mercian nedre, Northumbrian nedra), "a snake; the Serpent in the Garden of Eden," from Proto-Germanic *naethro "a snake" (source also of Old Norse naðra, Middle Dutch nadre, Old High German natra, German Natter, Gothic nadrs), from PIE root *nētr- "snake" (source also of Latin natrix "water snake" (the sense is probably by folk-association with nare "to swim"); Old Irish nathir, Welsh neidr "snake, serpent").

The modern form represents a faulty separation 14c.-16c. of a nadder into an adder, for which see also apron, auger, nickname, orange, humble pie, aitchbone, umpire. Nedder is still a northern English dialect form.

Since Middle English the word has been restricted to use as the common name of the viper, the only poisonous British reptile (though not generally fatal to humans), then by extension it was applied to venomous or similar snakes elsewhere (puff-adder, etc.). Folklore connection with deafness is via Psalms lviii.1-5. The adder is said to stop up its ears to avoid hearing the snake charmer called in to drive it away.

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.).

"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]

"snake which kills rats," 1818, from rat (n.) + snake (n.).

venomous serpent of the Americas noted for the rattle at the end of its tail, 1620s, from rattle + snake (n.).

RATTLE-SNAKE COCKTAIL.*

*So called because it will either cure Rattlesnake bite, or kill Rattlesnakes, or make you see them.

[Harry Craddock, "The Savoy Cocktail Book," 1930]

common name for a small gastropod on land or in fresh water, Middle English snail, from Old English snægl, from Proto-Germanic *snagila (source also of Old Saxon snegil, Old Norse snigill, Danish snegl, Swedish snigel, Middle High German snegel, dialectal German Schnegel, Old High German snecko, German Schnecke "snail").

This is reconstructed to be from *snog-, a variant of PIE root *sneg- "to crawl, creep; creeping thing" (see snake (n.)). The word essentially is a diminutive form of Old English snaca "snake," etymologically, "creeping thing."

Snail also formerly was used of slugs. Symbolic of slowness at least since c. 1000; snail's pace "very slow pace" is attested from c. 1400. Related: Snaily; snailish; snailing.

also snake-head, by 1837 as a type of North American plant used medicinally (also turtlehead; the form snake's head is attested from 1735); by 1883 as a type of carnivorous Southeast Asian freshwater fish, from snake (n.) + head (n.). Also in 19c. American English a name for railway rails that work lose and jut up, impaling or derailing passing cars (1838).

also snakestone, "fossil ammonite," 1660s, from snake (n.) + stone (n.). So-called from the old popular notion that they were snakes petrified while coiled.

1560s, "full of snakes" (originally of the hair of the Furies in classical mythology), from snake (n.) + -y (2). By 1580s as "of or resembling a snake." In Australia and New Zealand slang, "angry, annoyed" (1919). Snakish "of or pertaining to serpents" is from 1530s. The present-participle adjective snaking "winding, sinuous" is from 1590s.