Etymology
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bacteria (n.)

1847, plural of Modern Latin bacterium, from Greek bakterion "small staff," diminutive of baktron "stick, rod, staff, cudgel." So called because the first ones observed were rod-shaped. Introduced as a scientific word 1838 by German naturalist Christian Gottfried Ehrenberg. A classical plural sometimes also erroneously used as a singular.

The Greek word is from a PIE *bak- "staff used for support, peg" (compare Latin baculum "rod, walking stick;" Irish bacc, Welsh bach "hook, crooked staff;" Middle Dutch pegel "peg, pin, bolt"). De Vaan writes, "Since *b was very rare in PIE, and Celtic shows an unexplained geminate, we are probably dealing with a loanword from an unidentified source."

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linchpin (n.)
also linch-pin, "peg that holds a wheel on an axle" (now mainly figurative), late 14c., a corruption of linspin, literally "axle-pin," from pin (n.) + from Middle English lins "axle," from Proto-Germanic *luniso (source also of Old Saxon lunisa, Middle Dutch lunse, Dutch luns, German Lünse), a word of uncertain origin.
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warble (v.)
late 14c., from Old North French werbler "to sing with trills and quavers" (Old French guerbloiier), from Frankish *werbilon (cognate with Old High German wirbil "whirlwind," German Wirbel "whirl, whirlpool, tuning peg, vertebra," Middle Dutch wervelen "to turn, whirl"); see whirl (v.). Related: Warbled; warbling. The noun is recorded from late 14c.
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hobnail (n.)
"short, thick nail with a large head," 1590s, from nail (n.); the first element probably identical with hob "rounded peg or pin used as a mark or target in games" (1580s), which is of unknown origin. See hob. Because they were used to make heavy boots and shoes, the word was used figuratively for "rustic person" 17c. and after. Related: Hobnailed.
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thole (n.)
"peg," from Old English þoll "oar-pin," from Proto-Germanic *thulnaz (source also of Old Norse þollr, Middle Low German dolle, East Frisian dolle, Dutch dol), of unknown origin; according to Watkins probably from Proto-Germanic *thul-, from PIE root *teue- "to swell," on the notion of "a swelling." No record of the word in English from c. 1000 to mid-15c.
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*gembh- 

Proto-Indo-European root meaning "tooth, nail." 

It forms all or part of: cam (n.1) "projecting part of a rotating machinery;" comb; gem; oakum; unkempt.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit jambha-s "tooth;" Greek gomphos "peg, bolt, nail; a molar tooth;" Albanian dhemb "tooth;" Old English camb "comb." 

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snag (n.)
1570s, "stump of a tree, branch," of Scandinavian origin, compare Old Norse snagi "clothes peg," snaga "a kind of ax," snag-hyrndr "snag-cornered, with sharp points." The ground sense seems to be "a sharp protuberance." The meaning "sharp or jagged projection" is first recorded 1580s; especially "tree or branch in water and partly near the surface, so as to be dangerous to navigation" (1807). The figurative meaning "obstacle, impediment" is from 1829.
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hanger (n.)
early 15c., "one who hangs (something)," especially "executioner," later also "one who chooses pictures for an exhibition;" agent noun from hang (v.). Meaning "something that is suspended" is late 15c. Meaning "thing from which something is hung" is from 1690s. Meaning "loop or strap in a garment for hanging on a peg" is from 1680s; of wood or wire coat or dress hangers from 1873. Hanger-on is from 1540s.
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embolus (n.)
1660s, "stopper, wedge," from Latin embolus "piston of a pump," from Greek embolos "peg, stopper; anything pointed so as to be easily thrust in," also "a tongue (of land), beak (of a ship)," from emballein "to insert, throw in, invade" from assimilated form of en "in" (see en- (2)) + ballein "to throw" (from PIE root *gwele- "to throw, reach"). Medical sense in reference to obstruction of a blood vessel is from 1866. Related: Embolic.
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tap (n.1)
"stopper, faucet through which liquid can be drawn," Old English tæppa "tap, spigot," from Proto-Germanic *tappon (source also of Middle Dutch tappe, Dutch tap, Old High German zapfo, German Zapfe). Originally a tapering cylindrical peg for a cask, then a hollowed one to draw from it (compare sense evolution of spigot). Phrase on tap "ready for use, ready to be drawn and served" is recorded from late 15c. Tap-wrench, used in turning one, attested from 1815.
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