Etymology
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guard (n.)

early 15c., "one who keeps watch, a body of soldiers," also "care, custody, guardianship," and the name of a part of a piece of armor, from French garde "guardian, warden, keeper; watching, keeping, custody," from Old French garder "to keep, maintain, preserve, protect" (see guard (v.)). Abstract or collective sense of "a keeping, a custody" (as in bodyguard) also is from early 15c. Sword-play and fisticuffs sense is from 1590s; hence to be on guard (1640s) or off (one's) guard (1680s). As a football position, from 1889. Guard-rail attested from 1860, originally on railroad tracks and running beside the rail on the outside; the guide-rail running between the rails.

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guard (v.)

mid-15c., from guard (n.) or from Old French garder "to keep watch over, guard, protect, maintain, preserve" (corresponding to Old North French warder, see gu-), from Frankish *wardon, from Proto-Germanic *wardon "to guard" (from PIE root *wer- (3) "perceive, watch out for"). Italian guardare, Spanish guardar also are from Germanic. Related: Guarded; guarding.

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coast guard (n.)

also coast-guard, 1827, a guard stationed on a coast, originally to prevent smuggling, later serving as a general police force for the coast; see coast (n.) + guard (n.).

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guarded (adj.)
1560, "protected, defended," past-participle adjective from guard (v.). Meaning "reserved and cautious in speech, behavior, etc." is from 1728. Related: Guardedly; guardedness.
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bodyguard (n.)
also body-guard, 1735, "retinue, escort charged with the protection of one person," collective singular, from body + guard (n.). Attested 1861 as "a soldier of the bodyguard."
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lifeguard (n.)
also life-guard, 1640s, "a British monarch's bodyguard of soldiers," from life (n.) + guard (n.), translating German Leibgarde. Sense of "person paid to watch over bathers" is by 1891.
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vanguard (n.)

mid-15c., vaunt garde, from an Anglo-French variant of Old French avant-garde, from avant "in front" (see avant) + garde "guard" (see guard (n.)). Communist revolutionary sense is recorded from 1928.

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guardian (n.)

"one who guards," early 14c., garden; early 15c., gardein, from Anglo-French gardein (late 13c.), Old French gardien "keeper, custodian," earlier guarden, from Frankish *warding-, from the Germanic source of guard (v.). Specific legal sense is from 1510s. Guardian angel is from 1630s.

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safeguard (n.)

late 14c., sauf-gard, "protection, security, defense," from Old French sauve garde "safekeeping, safeguard" (13c.), from salve, sauve (fem. of sauf; see safe (adj.)) + garde "a keeping" (see guard (n.)). Meaning "one who protects, something that offers security from danger" is recorded from late 15c.

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blackguard (n.)

1530s, "scullion, kitchen knave," of uncertain origin. Perhaps in reference to military units or attendants so called for the color of their dress or their character; more likely originally a mock-military reference to scullions and kitchen-knaves of noble households, of black-liveried personal guards, and of shoeblacks. See black (adj.) + guard (n.). By 1736, sense had emerged of "one of the idle criminal class; man of coarse and offensive manners." Hence the adjectival use (1784), "of low or worthless character."

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