Etymology
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army (n.)

late 14c., armee, "armed expedition," from Old French armée "armed troop, armed expedition" (14c.), from Medieval Latin armata "armed force," from Latin armata, fem. of armatus "armed, equipped, in arms," as a noun, "armed men, soldiers," past participle of armare "to arm," literally "act of arming," related to arma "tools, arms" (see arm (n.2)).

Originally used of expeditions on sea or land; the restriction to "land force" is by late 18c. The transferred meaning "host, multitude" is by c. 1500. The meaning "body of men trained and equipped for war" is from 1550s.

The Old English words were here (still preserved in derivatives such as harrier; see harry (v.)), from Proto-Germanic *harjan, from PIE *korio- "people, crowd;" and fierd, with an original sense of "expedition," from Proto-Germanic *farthi-, related to faran "travel" (see fare (v.)). In spite of etymology, in the Anglo-Saxon Chronicle here generally meant "invading Vikings" and fierd was used for the local militias raised to fight them. Army-ant is from 1863, so called for marching in immense numbers.

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engineer (n.)

mid-14c., enginour, "constructor of military engines," from Old French engigneor "engineer, architect, maker of war-engines; schemer" (12c.), from Late Latin ingeniare (see engine); general sense of "inventor, designer" is recorded from early 15c.; civil sense, in reference to public works, is recorded from c. 1600 but not the common meaning of the word until 19c (hence lingering distinction as civil engineer). Meaning "locomotive driver" is first attested 1832, American English. A "maker of engines" in ancient Greece was a mekhanopoios.

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engineer (v.)

1818, "act as an engineer," from engineer (n.). Figurative sense of "arrange, contrive, guide or manage (via ingenuity or tact)" is attested from 1864, originally in a political context. Related: Engineered. Middle English had a verb engine "contrive, construct" (late 14c.), also "seduce, trick, deceive" (c. 1300) and "put to torture."

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re-engineer (v.)

"design and construct anew," 1944; see re- "back, again" + engineer (v.). Related: Re-engineered; re-engineering.

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millwright (n.)

"engineer who designs and builds mills and their machinery," late 15c., from mill (n.1) + wright.

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engineering (n.)

1720, "work done by an engineer," from engineer (n.). As a field of study, attested from 1792. An earlier word was engineership (1640s); engineery was attempted in 1793, but it did not stick.

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Braun 

German manufacturing company, named for founder Max Braun, mechanical engineer in Frankfurt am Main (1921).

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Wankel (n.)

type of rotary internal combustion engine, 1961, from name of German engineer Felix Wankel (1902-1988).

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theremin (n.)

electronic musical instrument, 1927, from the name of its inventor, Russian engineer Léon Thérémin (1896-1993).

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stratocracy (n.)

"government by the army, military government," 1650s, from Greek stratos "army, encamped army," literally "that which is spread out" (from PIE root *stere- "to spread"), + -cracy "rule or government by."

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