Etymology
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drill (n.1)

"tool for making holes in hard substances," 1610s, from Dutch dril, drille "a hole, instrument for boring holes," from drillen "to bore (a hole), turn around, whirl," from PIE root *tere- (1) "to rub, turn."

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drill (n.2)

"small furrow; trench or channel in which seeds are deposited," 1727; also "machine for sowing seeds" (1731), from obsolete drill "rill, trickling stream" (1640s), which is of unknown origin; perhaps connected to drill (n.1).

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drill (n.4)
"West African baboon species," 1640s, perhaps from a native word (compare mandrill).
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drill (n.3)

also drilling, kind of coarse, stout twilled cloth, 1743, from French drill, from German drillich "heavy, coarse cotton or linen fabric," from Old High German adjective drilich "threefold," from Latin trilix (genitive trilicis) "having three threads, triple-twilled," from tri- (see tri-) + licium "thread," a word of unknown etymology. So called in reference to the method of weaving it.

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drill (v.1)

"pierce or make a hole in with a drill or similar tool," c. 1600 (implied in drilling), from Dutch drillen "to bore (a hole), turn around, whirl," from Proto-Germanic *thr- (source also of Middle High German drillen "to turn, round off, bore," Old English þyrel "hole"), from PIE root *tere- (1) "to rub, turn," with derivatives referring to twisting, boring, and drilling. Related: Drilled, drilling. Compare thrill, the native English form of the word. Drill-press "drilling machine for boring holes in metal" is by 1850.

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drill (v.2)

"to instruct in military exercise," 1620s (a sense also found in Dutch drillen and the Danish and German cognates), probably from drill (v.1) on the notion of troops "turning" in maneuvers. Related: Drilled, drilling.

As a noun, "act of training soldiers in military tactics," 1630s; the extended sense of "the agreed-upon procedure" is by 1940. Drill-sergeant "non-commissioned officer who instructs soldiers in their duties and trains them in military movements" is by 1760. Drill-master "one who gives practical instructions in military tactics" is by 1766.

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fire-drill (n.)
1865, originally a device for making fire by the twirled stick method, from fire (n.) + drill (n.1). Meaning "rehearsal of what to do in a fire" is from 1884 (originally it also involved fighting the fire), from drill (n.) in the "agreed-upon procedure" sense (see drill (v.)).
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mandrill (n.)

"the largest, most hideous, and most ferocious of the baboons" [OED], 1744, perhaps ultimately from a West African language, but formed into the English components man (n.) + drill (n.4) "baboon," which is of West African origin. The earliest reference reports the name is what the animal was "called by the white men in this country [Sierra Leone], but why it is so called I know not, nor did I ever hear of the Name before, neither can those who call them so tell, except it be for their near Resemblance of a human Creature, though nothing at all like an Ape." [William Smith, "A New Voyage to Guinea"].  French mandrill, Spanish mandril seem to be from English.

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*tere- (1)

*terə-, Proto-Indo-European root meaning "to rub, turn," with derivatives referring to twisting, also to boring, drilling, piercing; and to the rubbing of cereal grain to remove the husks, and thus to threshing.

It forms all or part of: atresia; attorn; attorney; attrition; contour; contrite; detour; detriment; diatribe; drill (v.) "bore a hole;" lithotripsy; return; septentrion; thrash; thread; thresh; throw; threshold; trauma; trepan; tribadism; tribology; tribulation; trite; triticale; triturate; trout; trypsin; tryptophan; turn.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit turah "wounded, hurt;" Greek teirein "to rub, rub away;" Latin terere "to rub, thresh, grind, wear away," tornus "turning lathe;" Old Church Slavonic tiro "to rub;" Lithuanian trinu, trinti "to rub," Old Irish tarathar "borer," Welsh taraw "to strike."

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sidestep (n.)
also side-step, 1757, "a stepping to the side" (originally in military drill), from side (adj.) + step (n.). The verb is recorded from 1895; the figurative sense is attested from 1900.
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