WordNet (r) 3.0 (2006):

white flag
    n 1: flag consisting of a piece of white cloth that is hoisted
         to signal surrender or to ask for a truce [syn: white
         flag, flag of truce]

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "white flag":
   Roman candle, aid to navigation, alarm, amber light, balefire,
   beacon, beacon fire, bell, bell buoy, blinker, blue peter, buoy,
   calumet, caution light, downing of arms, empty hands,
   flag of truce, flare, fog bell, fog signal, fog whistle, foghorn,
   glance, go light, gong buoy, green light, hand of friendship,
   heliograph, high sign, international alphabet flag,
   international numeral pennant, kick, leer, marker beacon, nod,
   nudge, offer of parley, olive branch, outstretched hand,
   parachute flare, parley, peace feelers, peace offer,
   peace offering, peace pipe, pilot flag, pipe of peace, poke,
   police whistle, propitiatory gift, quarantine flag, radio beacon,
   red flag, red light, rocket, sailing aid, semaphore,
   semaphore flag, semaphore telegraph, sign, signal, signal beacon,
   signal bell, signal fire, signal flag, signal gong, signal gun,
   signal lamp, signal light, signal mast, signal post, signal rocket,
   signal shot, signal siren, signal tower, spar buoy, stop light,
   the nod, the wink, touch, traffic light, traffic signal,
   truce flag, watch fire, wigwag, wigwag flag, wink, yellow flag