The Collaborative International Dictionary of English v.0.48:

Befog \Be*fog"\, v. t. [imp. & p. p. Befogged; p. pr. & vb. n.
   Befogging.]
   1. To involve in a fog; -- mostly as a participle or part.
      adj.
      [1913 Webster]

   2. Hence: To confuse; to mystify.
      [1913 Webster]

WordNet (r) 3.0 (2006):

befog
    v 1: make less visible or unclear; "The stars are obscured by
         the clouds"; "the big elm tree obscures our view of the
         valley" [syn: obscure, befog, becloud, obnubilate,
         haze over, fog, cloud, mist]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "befog":
   becloud, bedim, bemist, bewilder, blanket, blind, blur, camouflage,
   cap, clabber up, cloak, cloud, cloud over, cloud up, conceal,
   confound, confuse, cover, cover up, curtain, darken, darken over,
   dim, disguise, dissemble, distract attention from, eclipse,
   encloud, enmist, ensconce, enshroud, envelop, fog, gloss over,
   haze, hide, keep under cover, mask, mist, muddy, nubilate,
   obfuscate, obnubilate, obscure, occult, overcast, overcloud,
   overshadow, oversmoke, perplex, pose, screen, shade, shadow,
   shroud, slur over, smog, smoke, stumble, varnish, veil,
   whitewash