The Collaborative International Dictionary of English v.0.48:

Flicker \Flick"er\ (fl[i^]k"[~e]r), v. i. [imp. & p. p.
   Flickered (fl[i^]k"[~e]rd); p. pr. & vb. n. Flickering.]
   [OE. flikeren, flekeren, to flutter, AS. flicerian,
   flicorian, cf. D. flikkeren to sparkle. [root]84. Cf.
   Flacker.]
   1. To flutter; to flap the wings without flying.
      [1913 Webster]

            And flickering on her nest made short essays to
            sing.                                 --Dryden.
      [1913 Webster]

   2. To waver unsteadily, like a flame in a current of air, or
      when about to expire; as, the flickering light.
      [1913 Webster]

            The shadows flicker to fro.           --Tennyson.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flicker \Flick"er\, n.
   1. The act of wavering or of fluttering; fluctuation; sudden
      and brief increase of brightness; as, the last flicker of
      the dying flame.
      [1913 Webster]

   2. (Zool.) The golden-winged woodpecker (Colaptes aurutus);
      -- so called from its spring note. Called also
      yellow-hammer, high-holder, pigeon woodpecker, and
      yucca.
      [1913 Webster]

            The cackle of the flicker among the oaks.
                                                  --Thoureau.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flicker
    n 1: a momentary flash of light [syn: flicker, spark,
         glint]
    2: North American woodpecker
    3: the act of moving back and forth [syn: waver, flutter,
       flicker]
    v 1: move back and forth very rapidly; "the candle flickered"
         [syn: flicker, waver, flitter, flutter, quiver]
    2: shine unsteadily; "The candle flickered" [syn: flicker,
       flick]
    3: flash intermittently; "The lights flicked on and off" [syn:
       flicker, flick]