Lewis Short
prosthĕsis | prŏthĕsis, is (noun F.f) : f., = πρόσθεσις, and , , f., = πρόθεσις
* A grammatical figure consisting in the prefixing of a letter or syllable to a word, prosthesis; as gnatus for natus, tetuli for tuli, Charis. 4; Diom. 2.
Charlton T. Lewis, Charles Short, A Latin Dictionary