Etymology
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armful (n.)

"as much as the arms can hold; what one can embrace," 1570s, from arm (n.1) + -ful.

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sidearm (adj.)

also side-arm, "done with the swing of the arm extended sideways," 1908, from side (adj.) + arm (n.1).

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arms race (n.)

1930, in reference to naval build-ups, from arms (see arm (n.2)) + race (n.1). First used in British English.

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forearm (v.)

"prepare for an attack," 1590s, from fore- + arm (v.) "take up weapons." Related: Forearmed; forearming.

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arms-length (n.)

"space equal to the length of a human arm," 1650s, from arm (n.1) + length. The figurative phrase at arm's end is recorded from 1570s.

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armory (n.)

c. 1300, armurie, "arms and weapons collectively; defensive armor;" see arm (n.2) + -ory and compare Old French armeurerie, armoirie. The meaning "place where arms are manufactured" is from mid-15c. (see armor + -y (1)). Also in Middle English as "arsenal, storehouse of weapons" (mid-15c.); the sense of "science of heraldry" (late 15c.) is from Old French armoierie, from armoier "to blazon," from Latin arma "weapons" (see arm (n.2)).

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armlet (n.)

1530s, "metal band or ring worn around the upper arm," diminutive of arm (n.1) with -let. Compare bracelet. The Latin word was armilla. As "a small intrusion of the sea into the land," also 1530s.

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firearm (n.)

also fire-arm, 1640s, from fire (n.) + arm (n.2). Anything which expels a missile by combustion of gunpowder (or a similar substance), from a pistol to a cannon. Related: Firearms.

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armament (n.)

1650s, "naval force equipped for war," from Latin armamentum "implement," from Latin armare "to arm, furnish with weapons" from arma "weapons" (including defensive armor), literally "tools, implements (of war);" see arm (n.2). The meaning "process of equipping for war" is from 1813.

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armchair (n.)

also arm-chair, "chair with rests for the elbows," 1630s, from arm (n.1) + chair (n.). Another old name for it was elbow-chair (1650s). The adjectival sense, in reference to "criticism of matters in which the critic takes no active part," is from 1879.

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