The Collaborative International Dictionary of English v.0.48:

Flinch \Flinch\, n.
   The act of flinching.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flinch \Flinch\, v. i. [imp. & p. p. Flinched; p. pr. & vb. n.
   Flinching.] [Prob. fr. OE. flecchen to waver, give way, F.
   fl['e]chir, fr. L. flectere to bend; but prob. influenced by
   E. blench. Cf. Flex.]
   1. To withdraw from any suffering or undertaking, from pain
      or danger; to fail in doing or perserving; to show signs
      of yielding or of suffering; to shrink; to wince; as, one
      of the parties flinched from the combat.
      [1913 Webster]

            A child, by a constant course of kindness, may be
            accustomed to bear very rough usage without
            flinching or complaining.             --Locke.
      [1913 Webster]

   2. (Croquet) To let the foot slip from a ball, when
      attempting to give a tight croquet.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flinch
    n 1: a reflex response to sudden pain [syn: wince, flinch]
    v 1: draw back, as with fear or pain; "she flinched when they
         showed the slaughtering of the calf" [syn: flinch,
         squinch, funk, cringe, shrink, wince, recoil,
         quail]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "flinch":
   avoid, avoidance, be startled, blanch, blench, blink, boggle,
   cower, cringe, demur, dodge, draw back, draw in, duck, elude,
   escape, eschew, evade, evasion, fade, fall back, fallback, falter,
   fight shy of, funk, hang back, hang off, have qualms, hesitate,
   hold off, jib, jump, jump a mile, make bones about, pause,
   pull back, pull in, pull out, pullback, pullout, quail, recede,
   recoil, reel back, retire, retract, retreat, scruple, sheer off,
   shrink, shrink back, shrink from, shun, shy, shy at, sidestep,
   sidestepping, squinch, start, start aside, start back, startle,
   stick at, stickle, strain, swerve, turn aside, waver, weasel,
   weasel out, wince, withdraw