Source : Webster's Revised Unabridged Dictionary (1913)

Vanguard \Van"guard`\, n. [For vantguard, avantguard, F.
   avant-garde; avant before, fore + garde guard. See {Avant},
   {Ab-},{Ante-}, and {Guard}, and cf. {Advance}, {Vamp}, {Van}
   of an army, {Vaward}.] (Mil.)
   The troops who march in front of an army; the advance guard;
   the van.

Source : WordNet®

vanguard
     n 1: the leading units moving at the head of an army [syn: {van}]
     2: any creative group active in the innovation and application
        of new concepts and techniques in a given field
        (especially in the arts) [syn: {avant-garde}, {van}, {new
        wave}]
     3: the position of greatest advancement; the leading position
        in any movement or field [syn: {forefront}, {cutting edge}]