prothesis

In linguistics, prothesis (/ˈprɒθɪsɪs/; from post-classical Latin based on Ancient Greek: πρόθεσις próthesis 'placing before'), or less commonly prosthesis (from Ancient Greek πρόσθεσις prósthesis 'addition'), is the addition of a sound or syllable at the beginning of a word without changing the word's meaning or the rest of its structure. A vowel or consonant added by prothesis is called prothetic or less commonly prosthetic.

Prothesis is different from the adding of a prefix, which changes the meaning of a word.