The Collaborative International Dictionary of English v.0.48:

Nasalize \Na"sal*ize\, v. t. [imp. & p. p. Nasalized; p. pr. &
   vb. n. Nasalizing.]
   To render nasal, as sound; to insert a nasal or sound in.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Nasalize \Na"sal*ize\, v. t.
   To utter words or letters with a nasal sound; to speak
   through the nose; to pronounce with a lowered velum.
   [1913 Webster + WordNet 1.5]

WordNet (r) 3.0 (2006):

nasalize
    v 1: speak nasally or through the nose; "In this part of the
         country, people tend to nasalize" [syn: nasalize,
         nasalise]
    2: pronounce with a lowered velum; "She nasalizes all her
       vowels" [syn: nasalize, nasalise]