The Collaborative International Dictionary of English v.0.48:

Uglify \Ug"li*fy\, v. t. [Ugly + -fy.]
   To disfigure; to make ugly. [R.] --Mad. D'Arblay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

uglify
    v 1: make ugly [ant: beautify, embellish, fancify,
         prettify]