vanguard (n.)

French, literally "before," in various terms borrowed into English; cognate with Italian avanti, both from Late Latin abante, a compound of ab "from" (see ab-) and ante "before, in front of" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before") which meant "from in front of," but in Vulgar Latin came to mean simply "before."

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.