The Collaborative International Dictionary of English v.0.48:

Wigwag \Wig"wag`\, v. i. [See Wag, v. t.] (Naut.)
   To signal by means of a flag waved from side to side
   according to a code adopted for the purpose. [Colloq.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Wigwag \Wig"wag`\, v. t. & i. [imp. & p. p. Wigwagged; p. pr.
   & vb. n. Wigwagging.]
   To move to and fro, to wag.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Wigwag \Wig"wag`\, n. [See Wigwag, v. t. & i.]
   Act or art of wigwagging; a message wigwagged; -- chiefly
   attributive; as, the wigwag code. -- Wig"wag`er, n.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

wigwag
    v 1: send a signal by waving a flag or a light according to a
         certain code
    2: signal by or as if by a flag or light waved according to a
       code

Moby Thesaurus II by Grady Ward, 1.0:

116 Moby Thesaurus words for "wigwag":
   Lissajous figure, Roman candle, aid to navigation, alarm,
   alternate, alternation, amber light, back and fill, back-and-forth,
   balefire, battledore and shuttlecock, beacon, beacon fire, bell,
   bell buoy, blinker, blue peter, brandish, buoy, caution light,
   come and go, coming and going, ebb and flow, flap, flare, flaunt,
   float, flourish, flutter, flux and reflux, fly, fog bell,
   fog signal, fog whistle, foghorn, glance, go light, gong buoy,
   green light, heliograph, high sign, hitch and hike,
   international alphabet flag, international numeral pennant, kick,
   leer, marker beacon, nod, nudge, parachute flare, pass and repass,
   pilot flag, poke, police whistle, quarantine flag, radio beacon,
   reciprocate, reciprocation, red flag, red light, rhythmic play,
   ride and tie, rocket, sailing aid, seesaw, seesawing, semaphore,
   semaphore flag, semaphore telegraph, shake, shuttle, shuttlecock,
   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, sine wave, spar buoy, stop light, swing, teeter,
   teeter-totter, teeter-tottering, teetering, the nod, the wink,
   to-and-fro, tottering, touch, traffic light, traffic signal,
   undulate, ups and downs, wag, watch fire, wave, wax and wane,
   white flag, wibble-wabble, wield, wigwag flag, wink, yellow flag,
   zigzag