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]