Pronunciation GB: prɒsˈθiːsɪs, GA: prɑsˈθiːsɪs

The addition of a sound at the beginning of a word. An example is t-prosthesis in Irish. After the definite article t is added to a masculine noun beginning with a vowel or s, so “the water” is an t-uisge and “the priest” is an t-sagairt.

Also called prothesis.