The Collaborative International Dictionary of English v.0.48:

Bedim \Be*dim"\ (b[-e]*d[i^]m"), v. t. [imp. & p. p. Bedimmed
   (b[-e]*d[i^]md"); p. pr. & vb. n. Bedimming.]
   To make dim; to obscure or darken. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bedim
    v 1: make darker and difficult to perceive by sight [syn:
         benight, bedim]
    2: make obscure or unclear; "The distinction was obscured" [syn:
       obscure, bedim, overcloud]