The Collaborative International Dictionary of English v.0.48:

Intimidate \In*tim"i*date\, v. t. [imp. & p. p. Intimidated;
   p. pr. & vb. n. Intimidating.] [LL. intimidatus, p. p. of
   intimidare to frighten; pref. in- in + timidus fearful,
   timid: cf. F. intimider. See Timid.]
   To make timid or fearful; to inspire of affect with fear; to
   deter, as by threats; to dishearten; to abash.
   [1913 Webster]

         Now guilt, once harbored in the conscious breast,
         Intimidates the brave, degrades the great. --Johnson.

   Syn: To dishearten; dispirit; abash; deter; frighten;
        terrify; daunt; cow.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

intimidating \intimidating\ adj.
   discouraging; inhibiting; deterring. Opposite of
   encouraging.

   Syn: daunting.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

intimidating
    adj 1: discouraging through fear [syn: daunting,
           intimidating]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "intimidating":
   abusive, admonitory, bludgeoning, blustering, browbeating,
   bulldozing, bullying, cautionary, comminatory, denunciatory,
   deterrent, discouraging, disinclining, dissuading, dissuasive,
   expostulatory, fear-inspiring, foreboding, hectoring, imminent,
   lowering, menacing, minacious, minatory, monitory, ominous,
   terroristic, terrorizing, threatening, threatful