early 15c., "one who keeps watch," from Middle French garde "guardian, warden, keeper; watching, keeping, custody," from Old French garder "to keep, maintain, preserve, protect" (corresponding to Old North French warder, see gu-), from Frankish *wardon, from Proto-Germanic *wardo- "to guard" (see ward, 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. Guard-rail attested from 1860.

mid-15c., from guard, n. or from Old French garder "to keep watch over, guard, protect." Related: Guarded; guarding.