Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

epenthesis
     n : 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"
     [also: {epentheses} (pl)]