Online Etymology Dictionary

pip (n.3): "spot on a playing card, etc." c. 1600, peep, of unknown origin. Because of the original form, it is not considered as connected to pip (n.1). Related: Pips.
pip (n.2): "disease of birds," late 14c., probably from Middle Dutch pippe "mucus," from West Germanic *pipit (source also of East Frisian pip, Middle High German pfipfiz, German Pips), an early borrowing from Vulgar Latin *pippita, unexplained alteration of Latin pituita "phlegm" (see pituitary).
pip (n.1): "seed of an apple," 1797, shortened form of pipin "seed of a fleshy fruit" (early 14c.), from Old French pepin (13c.), probably from a root *pipp-, expressing smallness (compare Italian pippolo, Spanish pepita "seed, kernel").
pip-pip: slangy salutation current in Britain c. 1907-1923, said by Partridge to be in imitation of bicycle horn noise.
pippin (n.): "excellent person or thing," 1897, from coveted varieties of apple that were raised from seed (so called since early 15c.), from Middle English pipin "seed" (see pip (n.1)).
pipsqueak (n.): also pip-squeak, 1910, from the trivial noise a young or weak creature makes.
pipe (n.1): Old English pipe "musical wind instrument," also "tube to convey water," from Vulgar Latin *pipa "a pipe, tube-shaped musical instrument" (source also of Italian pipa, French pipe, Old Frisian pipe, German Pfeife, Danish pibe, Swedish pipa, Dutch pijp), a back-formation from Latin pipare "to chirp or peep," of imitative origin. All tubular senses ultimately derive from "small reed, whistle." Meaning "device for smoking" first recorded 1590s. Pipe-bomb attested from 1960. Pipe-cleaner recorded from 1863.
pipeline (n.): 1859, "continuous line of pipes," from pipe (n.1) + line (n.). Figurative sense of "channel of communication" is from 1921; surfer slang meaning "hollow part of a large wave" is attested by 1963.
pipette (n.): also pipet, 1818, from French pipette, from Middle French pipette "tube," diminutive of Old French pipe, from Vulgar Latin *pipa (see pipe (n.1)).
water-pipe (n.): c. 1400, "conduit for water," from water (n.1) + pipe (n.1). The smoking sense is first attested 1824.
pitch-pipe (n.): 1711, from pitch (n.) in the musical sense + pipe (n.1).
piper (n.): Old English pipere, agent noun from pipe (v.). As a kind of fish, from c. 1600. Expression pay the piper recorded from 1680s.
pipe dream (n.): 1870; the sort of improbable fantasy one has while smoking opium; from pipe (n.1) + dream (n.). Old English pipdream meant "piping."
blow-pipe (n.): type of weapon, 1680s, from blow (v.1) + pipe (n.1).
pipe (v.): Old English pipian "to play on a pipe," from Latin pipare "to peep, chirp" (see pipe (n.1)). Compare Dutch pijpen, German pfeifen. Meaning "convey through pipes" is first recorded 1887. Related: Piped; piping. Piping hot is in Chaucer, a reference to hissing of food in a frying pan; to pipe up (early 15c.) originally meant "to begin to play" (on a musical instrument); sense of "to speak out" is from 1856. Pipe down "be quiet" is from 1900, probably a reversal of this, but earlier (and concurrently) in nautical jargon it was a bo'sun's whistle signal to dismiss the men from duty (1833).
pipes (n.): "voice," 1580s, from pipe (n.1).
pipe (n.2): type of cask, early 14c., from Old French pipe "liquid measure, cask for wine," from a special use of Vulgar Latin *pipa "pipe" (see pipe (n.1)).
stove-pipe (n.): 1690s, from stove (n.) + pipe (n.). As a type of hat for men, from 1851, so called for being tall and cylindrical like a stove-pipe.
stand-pipe (n.): "upright pipe," in various technical senses, 1810, from stand (v.) + pipe (n.).
tail-pipe (n.): also tailpipe, 1757, "small pipe fixed at the swell of a musket to receive the ramrod," from tail (n.1) + pipe (n.). From 1832 as "suction pipe of a pump;" 1907 as "exhaust pipe of an automobile."
kernel (n.): "edible substance in a nut or the stone of a fruit," Old English cyrnel "seed, kernel, pip," from Proto-Germanic *kurnilo- (source also of Middle High German kornel "a grain," Middle Dutch cornel "coarse meal"), from the root of corn "seed, grain" (see corn (n.1)) + -el, diminutive suffix. Figurative sense of "core or central part of anything" is from 1550s.
ace (n.): c. 1300, "one at dice," from Old French as "one at dice," from Latin as "a unit, one, a whole, unity;" also the name of a small Roman coin ("originally one pound of copper; reduced by depreciation to half an ounce" [Lewis]), perhaps originally Etruscan and related to Greek eis "one" (from PIE *sem- "one, as one"), or directly from the Greek word.

In English, it meant the side of the die with only one mark before it meant the playing card with one pip (1530s). Because this was the lowest roll at dice, ace was used metaphorically in Middle English for "bad luck" or "something of no value;" but as the ace is often the highest playing card, the extended senses based on "excellence, good quality" arose 18c. as card-playing became popular. Ace in the hole in the figurative sense of "concealed advantage" is attested from 1904, from crooked stud poker deals.

Meaning "outstanding pilot" dates from 1917 (technically, in World War I aviators' jargon, one who has brought down 10 enemy planes, though originally in reference to 5 shot down), from French l'ace (1915), which, according to Bruce Robertson (ed.) "Air Aces of the 1914-1918 War" was used in prewar French sporting publications for "top of the deck" boxers, cyclists, etc. Sports meaning of "point scored" (1819) led to that of "unreturnable serve" (1889).
grain (n.): early 14c., "a small, hard seed," especially of one of the cereal plants, also as a collective singular, "seed of wheat and allied grasses used as food;" also "something resembling grain; a hard particle of other substances" (salt, sand, later gunpowder, etc.), from Old French grain, grein (12c.) "seed, grain; particle, drop; berry; grain as a unit of weight," from Latin granum "seed, a grain, small kernel," from PIE root *gre-no- "grain" (see corn (n.1)). From late 14c. as "a species of cereal plant." In the U.S., where corn has a specialized sense, it is the general word (used of wheat, rye, oats, barley, etc.).

Figuratively, "the smallest possible quantity," from late 14c. From early 15c. in English as the smallest unit of weight (originally the weight of a plump, dry grain of wheat or barley from the middle of the ear). From late 14c as "roughness of surface; a roughness as of grains." In reference to wood, "quality due to the character or arrangement of its fibers," 1560s; hence, against the grain (1650), a metaphor from carpentry: cutting across the fibers of the wood is more difficult than cutting along them.

Earliest sense of the word in English was "scarlet dye made from insects" (early 13c.), a sense also in the Old French collateral form graine; see kermes for the evolution of this sense, which was frequent in Middle English; also compare engrain. In Middle English grain also could mean "seed of flowers; pip of an apple, grape, etc.; a berry, legume, nut." Grain alcohol attested by 1854.