Online Etymology Dictionary

tachometer (n.): 1810, from Greek tachos "speed" + -meter.
tachy-: word-forming element meaning "rapid, swift, fast," from Latinized comb. form of Greek takhy "swift."
tachycardia (n.): 1868, Modern Latin, coined 1867 by German-born physician Hermann Lebert (1813-1878) from tachy- "swift" + kardia "heart" (see cardiac).
tachymeter (n.): 1836, from tachy- "swift" + -meter.
M. GAETANO CAÏRO has invented an instrument, to which he has given the name of Tachymeter (rapid measurer). Its object is to give the area of plane surfaces bounded by any outline whatever, without the necessity of any arithmetical operation. ["Magazine of Popular Science and Journal of the Useful Arts," Volume 2, 1836]
tachyon (n.): 1967, hypothetical faster-than-light particle, from tachy- "swift" + -on.
tachypnea (n.): "hysterical rapid breathing," 1896, from tachy- "swift" + -pnea, from pnein "to breathe" (see pneuma). Related: Tachypneic.
tacit (n.): c.1600, from French tacite, from Latin tacitus "that is passed over in silence, done without words, assumed, silent," prop. past participle of tacere "to be silent," from PIE root *tak- "to be silent" (cf. Gothic þahan, Old Norse þegja "to be silent," Old Norse þagna "to grow dumb," Old Saxon thagian, Old High German dagen "to be silent"). The musical instruction tacet is the 3rd person present singular of the Latin verb.
taciturn (adj.): "habitually silent," 1771, back-formation from taciturnity.
taciturnity (n.): mid-15c., from Middle French taciturnité, from Latin taciturnitatem (nominative taciturnitas) "a being or keeping silent," from taciturnus "disposed to be silent," from tacitus "silent" (see tacit).
tack (n.1): "clasp, hook, fastener," also "a nail of some kind," late 13c., from Old North French taque "nail, pin, peg," probably from a Germanic source (cf. Middle Dutch tacke "twig, spike," Low German takk "tine, pointed thing," German Zacken "sharp point, tooth, prong"); perhaps related to tail. Meaning "small, sharp nail with a flat head" is attested from mid-15c. The meaning "rope to hold the corner of a sail in place" is first recorded late 14c.
tack (v.1): late 14c., "to attach with a nail, etc.," from tack (n.1). Meaning "to attach as a supplement" (with suggestion of hasty or arbitrary proceeding) is from 1680s. Related: Tacked; tacking.
tack (n.2): "horse's harness, etc.," 1924, shortening of tackle (n.) in sense of "equipment." Tack in a non-equestrian sense as a shortening of tackle is recorded in dialect from 1777.
tack (n.3): "food," 1833, perhaps a shortening and special use of tackle (n.) in the sense of "gear."
tack (v.2): "sail into the wind," 1550s, from tack (n.1) in the sailing sense. Figurative sense of "course or line of conduct or action" is from 1670s. Related: Tacked; tacking.
tackle (n.): mid-13c., "apparatus, gear," from Middle Dutch or Middle Low German takel "the rigging of a ship," perhaps related to Middle Dutch taken "grasp, seize" (see take (v.)), or perhaps from root of tack (n.1). Meaning "apparatus for fishing" is recorded from late 14c. The noun meaning "act of tackling" in the sporting sense is recorded from 1876 (see tackle (v.)); as the name of a position in North American football, it is recorded from 1884.
tackle (v.): mid-14c., "entangle, involve," from tackle (n.). Sense of "to furnish (a ship) with tackles" is from c.1400; meaning "to harness a horse" is recorded from 1714. The meaning "lay hold of, come to grips with, attack" is attested from 1828, described by Webster that year as "a common popular use of the word in New England, though not elegant;" figurative sense of "try to deal with" (a task or problem) is from 1840. The verb in the sporting sense first recorded 1867. Related: Tackled; tackling.
tacky (adj.1): "sticky," 1788, from tack (n.1) in the sense of "an act of attaching temporarily" + -y (2).
tacky (adj.2): "in poor taste," 1862, adj. use of tackey (n.) "small or inferior horse" (1800), later "hillbilly, cracker" (1888), of uncertain origin.
taco (n.): tortilla filled with spiced meat, etc., 1949, from Mexican Spanish, "light lunch," literally "plug, wadding."
tact (n.): 1650s, "sense of touch or feeling" (with an isolated instance from c.1200), from Latin tactus "touch, feeling, handling, sense of touch," from root of tangere "to touch" (see tangent). Meaning "sense of "discernment, diplomacy, etc." first recorded 1804, from a sense that developed in French cognate tact.
tactful (adj.): 1864, from tact + -ful. Related: Tactfully; tactfulness.
tactic (n.): 1766, from Modern Latin tactica, from Greek taktike (tekhne) "(art of) arrangement," from fem. of taktikos (see tactics). Earlier it meant "a tactician" (1630s), and was in use as an adjective meaning "tactical" (c.1600).
tactical (adj.): 1560s, from Modern Latin tactica (see tactics); in reference to nuclear weapons (opposed to strategic) it is recorded from 1957. Related: Tactically.
tactician (n.): 1761, from tactic + -ian.
tactics (n.): 1620s, from Modern Latin tactica (17c.), from Greek taktike techne "art of arrangement," noun use of fem. of taktikos "of or pertaining to arrangement," especially "tactics in war," adjective to taxis "order," verbal noun of tassein "arrange," from PIE root *tag- "to set aright."
tactile (adj.): 1610s, "perceptible to touch," from French tactile, from Latin tactilis "tangible, that may be touched," from tactus, past participle of tangere "to touch" (see tangent). Meaning "of or pertaining to touch" is attested from 1650s.
tactless (adj.): 1847, from tact + -less. Related: Tactlessly; tactlessness.
tactual (adj.): 1640s, from Latin tactus "touch" (see tactile) + -al (1).
tad (n.): 1877, "young or small child," probably a shortened form of tadpole, which is said to be the source of Tad as the nickname of U.S. President Lincoln's son Thomas (1853–1871). The extended meaning "small amount" is first recorded 1915.
tadpole (n.): c.1400, from tadde "toad" (see toad) + pol "head" (see poll (n.)).
tae kwon do: 1967, from Korean, from tae "kick" + kwon "fist" + do "art, way, method."
taffeta (n.): late 14c., from Old French taffetas (early 14c.), from Italian taffeta, ultimately from Persian taftah "silk or linen cloth," noun use of taftah, past participle of taftan "to shine," also "to twist, spin." Applied to different fabrics at different times (and cf. tapestry).
taffrail (n.): 1814, alteration of tafferel "upper panel on the stern of a ship (often ornamented)" (1704), earlier, "a carved panel" (1620s), from Dutch tafereel "panel for painting or carving," dissimulation from *tafeleel, diminutive of tafel "table," from the general West Germanic borrowing of Latin tabula "slab, board" (see table (n.)). The word developed in Dutch from the custom of ornamenting the high, flat stern of old sailing ships; spelling and sense altered in English by influence of rail (n.).
taffy (n.): candy made from sugar or molasses, 1817, related to toffee, but of uncertain origin; perhaps associated with tafia (1763), a rum-like alcoholic liquor distilled from molasses, presumably of W.Indian or Malay origin (perhaps a Creole shortening of ratafia). On this theory, the candy would have been made from the syrup skimmed off the liquor during distillation.
Taffy: characteristic name of a Welshman, c.1700, from Teifi, Welsh corruption of David (q.v.).
Taft: surname, from a variant of Old English toft "homestead, site of a house."
tag (n.1): "small hanging piece from a garment," c.1400, perhaps from a Scandinavian source (cf. Norwegian tagg "point, prong, barb," Swedish tagg "prickle, thorn," Middle Low German tagge "branch, twig, spike"); cognate with tack (n.1). Meaning "label" is first recorded 1835; sense of "automobile license plate" is recorded from 1935, originally underworld slang. Meaning "an epithet, popular designation" is recorded from 1961, hence slang verb meaning "to write graffiti in public places" (1990).
tag (n.2): "children's game," 1738, perhaps a variation of Scot. tig "touch, tap" (1721), probably an alteration of Middle English tek "touch, tap" (see tick (2)).
tag (v.1): "to furnish with a tag," mid-15c., from tag (n.1). Related: Tagged; tagging. To tag along is first recorded 1900.
tag (v.2): in the baseball sense, 1907, from tag (n.2); the adjective in the pro-wrestling sense is recorded from 1955.
Tagalog (n.): people living near Manila in the Philippines, also their language, 1704, from Tagalog taga "native to" + ilog "river."
tagliatelle (n.): 1876, from Italian tagliatelle, plural noun from tagliare "to cut" (see entail).
tagline (n.): "punchline of a joke," 1926, originally "last line in an actor's speech" (1916), from tag (n.1) + line (n.).
tahini: from Arabic tahina, from tahana "to grind or crush."
Tahoe: Lake on the Nevada-California border, from Washo /da'aw/ "lake."
tai chi: 1736, the "supreme ultimate" in Taoism and Neo-Confucianism, from Chinese tai "extreme" + ji "limit." The form of martial arts training (said to have been developed by a priest in the Sung dynasty, 960-1279) is first attested 1962, in full, tai chi ch'uan, with Chinese quan "fist."
taiga (n.): belt of coniferous forests in Siberia, 1869, from Russian taiga, which is of Mongolian origin.
tail (n.1): "hindmost part of an animal," Old English tægl, tægel, from Proto-Germanic *tagla- (cf. Old High German zagal, German Zagel "tail," dialectal German Zagel "penis," Old Norse tagl "horse's tail"), from PIE *doklos, from root *dek- "something long and thin" (referring to such things as fringe, lock of hair, horsetail; cf. Old Irish dual "lock of hair," Sanskrit dasah "fringe, wick").

The primary sense, at least in Germanic, seems to have been "hairy tail," or just "tuft of hair," but already in Old English the word was applied to the hairless "tails" of worms, bees, etc. Another Old English word for "tail" was steort (see stark). Meaning "reverse side of a coin" is from 1680s; that of "backside of a person, buttocks" is recorded from c.1300; slang sense of "pudenda" is from mid-14c.; that of "woman as sex object" is from 1933, earlier "prostitute" (1846). The tail-race (1776) is the part of a mill race below the wheel. To turn tail "take flight" (1580s) originally was a term in falconry. The image of the tail wagging the dog is attested from 1907.
tail (n.2): "limitation of ownership," a legal term, early 14c. in Anglo-French; late 13c. in Anglo-Latin, in most cases a shortened form of entail.
tail (v.): "follow secretly," U.S. colloquial, 1907, is from earlier sense of "follow or drive cattle," from tail (n.1). Related: Tailed; tailing. Tail off "diminish" is attested from 1854.