guard:  Prehistoric West Germanic *warthōn produced English ward. It was borrowed into Vulgar Latin as *wardāre, and following the general phonetic trend by which Germanic initial w became g(u) in the Romance languages, it produced Italian guardare, Spanish guardar, and French garder. The noun derived from the latter, garde, gave English guard. Guardian , borrowed from Old French gardien, has a doublet in warden. => ward
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 Middle 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.
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" (see ward (v.)). Italian guardare, Spanish guardar also are from Germanic. Related: Guarded; guarding.