epenthesis

from WordNet (r) 3.0 (2006)

epenthesis
    n 1: the insertion of a vowel or consonant into a word to make
         its pronunciation easier; "the insertion of a vowel in the
         plural of the word `bush' is epenthesis"

from The Collaborative International Dictionary of English v.0.48

Epenthesis \E*pen"the*sis\, n.; pl. {Epentheses}. [L., fr. Gr.
   ?; 'epi` + ? to put or set in.] (Gram.)
   The insertion of a letter or a sound in the body of a word;
   as, the b in "nimble" from AS. n[=e]mol.
   [1913 Webster]