The Collaborative International Dictionary of English v.0.48:

Shudder \Shud"der\, v. i. [imp. & p. p. Shuddered;p. pr. & vb.
   n. Shuddering.] [OE. shoderen, schuderen; akin to LG.
   schuddern, D. schudden to shake, OS. skuddian, G. schaudern
   to shudder, sch["u]tteln to shake, sch["u]tten to pour, to
   shed, OHG. scutten, scuten, to shake.]
   To tremble or shake with fear, horrer, or aversion; to shiver
   with cold; to quake. "With shuddering horror pale." --Milton.
   [1913 Webster]

         The shuddering tennant of the frigid zone. --Goldsmith.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Shudder \Shud"der\, n.
   The act of shuddering, as with fear. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

shudder
    n 1: an almost pleasurable sensation of fright; "a frisson of
         surprise shot through him" [syn: frisson, shiver,
         chill, quiver, shudder, thrill, tingle]
    2: an involuntary vibration (as if from illness or fear) [syn:
       tremor, shudder]
    v 1: shake, as from cold; "The children are shivering--turn on
         the heat!" [syn: shiver, shudder]
    2: tremble convulsively, as from fear or excitement [syn:
       shudder, shiver, throb, thrill]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "shudder":
   bang, be cold, bob, bobble, boot, bounce, bump, charge, chatter,
   chill, convulse, convulsion, didder, disquiet, disquietude, dither,
   dithers, falter, fidgetiness, fidgets, flush, flutter, freeze,
   freeze to death, grimace, grow cold, gyrate, have a chill,
   have an ague, have goose pimples, heaving, horripilate, hustle,
   inquietude, jactitate, jar, jerk, jig, jigget, jiggle, jog, joggle,
   jollies, jolt, jostle, jounce, jump, kick, lift, lose heat,
   palpitation, panting, paroxysm, perish with cold, pitapat,
   pitter-patter, quake, quaking, quaver, quavering, quiver,
   quivering, rattle, restlessness, rictus, rush, rush of emotion,
   sensation, shake, shakes, shaking, shimmy, shiver, shivers, shock,
   spasm, surge of emotion, thrill, throb, throbbing, tic, tingle,
   tingling, titillation, tremble, trembling, tremor,
   tremor of excitement, trepidation, trepidity, twitch, twitter,
   unrest, vibrate, vibration, wobble