Etymology
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side-arms (n.)

also sidearms, "military weapons worn at the side or at the belt" (sword, dagger, etc.), 1760, from side (adj.) + plural of arm (n.2). Especially of the swords of officers, which they may be allowed to keep in a surrender.

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underarm (adj.)

1816, "underhand" (in reference to a style of throwing), from under + arm (n.1). First attested 1908 in dressmaking sense of "seams on the lower half of the arm-hole;" as a euphemism for armpit, it is attested from 1930s, popularized by advertisers.

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unarmed (adj.)

c. 1300, "with armor removed," from un- (1) "not" + armed, or else past-participle adjective from unarm "strip of armor" (c. 1300), from un- (2) "opposite of" + arm (v.). Meaning "not fitted to attack, weaponless" is from late 14c.

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armadillo (n.)

burrowing mammal of the American tropics, 1570s, from Spanish armadillo, diminutive of armado "armored," from Latin armatus, past participle of armare "to arm, furnish with weapons," from arma "weapons" (including defensive armor), literally "tools, implements (of war);" see arm (n.2). The animal is so called for its hard, plated shell.

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armature (n.)

c. 1400, "an armed force," from Latin armatura "armor, equipment," from armatus, past participle of armare "to arm, furnish with weapons" from arma "weapons," literally "tools, implements (of war);" see arm (n.2). The meaning "armor" is mid-15c.; that of "protective covering of a plant or animal" is from 1660s. The electromagnetic sense is from 1835.

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rearm (v.)

also re-arm, "provide with a new supply of weapons; acquire a new supply of weapons," 1805 (implied in rearming), from re- "back, again" + arm (v.) "to take up arms; supply with arms." In 20c., especially "to acquire more advanced weapons." Related: Rearmed.

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armpit (n.)

mid-14c., "hollow place under the shoulder," from arm (n.1) + pit (n.1). Arm-hole (early 14c.) was used in this sense but was obsolete by 18c. Another Middle English word was asselle (early 15c.), from Old French asselle, from Latin axilla. The colloquial phrase armpit of the nation for any locale regarded as ugly and disgusting was in use by 1965.

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armoire (n.)

"large wardrobe with doors and shelves," 1570s, from French armoire, from Old French armarie "cupboard, bookcase, reliquary" (12c., Modern French armoire), from Latin armarium "closet, chest, place for implements or tools," from arma "gear, tools, ship's tackle, weapons of war" (see arm (n.2)). The French word was borrowed earlier as ambry (late 14c.).

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coat of arms (n.)

mid-14c., also simply coat (mid-14c.); originally a tunic embroidered or painted with heraldic armorial bearings (worn over armor, etc); see coat (n.) + arm (n.2) and compare Old French cote a armer. Sense transferred in Middle English to the heraldic arms themselves. Hence turncoat, one who put his coat on inside-out to hide the badge of his loyalty (1550s).

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disarm (v.)

late 14c., "deprive of power to injure or terrify, render harmless," a figurative sense, from Old French desarmer (11c.), from des- "reverse of" (see dis-) + armer "to arm" (see arm (v.)). The literal senses "deprive of weapons" (transitive), "put off one's armor or lay down one's weapons" (intransitive) are early 15c. Related: Disarmed; disarming; disarmingly.

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