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]