The Collaborative International Dictionary
Epithesis
Epithesis \E*pith"e*sis\, n. [NL., fr. Gr. ? a putting on; 'epi` upon + ? to place.] The addition of a letter at the end of a word, without changing its sense; as, numb for num, whilst for whiles.
Wiktionary
epithesis
n. (context linguistics English) The addition of a letter or sound at the end of a word, without changing its meaning, as in "numb" for "num" or "whilst" for "whiles".