The Collaborative International Dictionary of English v.0.48:

Guerilla \Gue*ril"la\, a.
   See Guerrilla.
   [1913 Webster]

WordNet (r) 3.0 (2006):

guerilla
    n 1: a member of an irregular armed force that fights a stronger
         force by sabotage and harassment [syn: guerrilla,
         guerilla, irregular, insurgent]