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]