The Collaborative International Dictionary of English v.0.48:

Infantry \In"fan*try\, n. [F. infanterie, It. infanteria, fr.
   infante infant, child, boy servant, foot soldier, fr. L.
   infans, -antis, child; foot soldiers being formerly the
   servants and followers of knights. See Infant.]
   [1913 Webster]
   1. A body of children. [Obs.] --B. Jonson.
      [1913 Webster]

   2. (Mil.) A body of soldiers serving on foot; foot soldiers,
      in distinction from cavalry.
      [1913 Webster]

WordNet (r) 3.0 (2006):

infantry
    n 1: an army unit consisting of soldiers who fight on foot;
         "there came ten thousand horsemen and as many fully-armed
         foot" [syn: infantry, foot]