(phonology) The prepending of phonemes at the beginning of a word without changing its morphological structure, as in Spanish esfera from Latin sphaera (“sphere”) (without prothesis the word would have become *sfera).

(Christianity) The preparation and preliminary oblation of the Eucharistic bread and wine in the Divine Liturgy of the Eastern Orthodx and Eastern Catholic Churches. / (by extension) Credence table.

(phonology) The prothesis of the sound /h/ to words beginning with a vowel, especially as found in Celtic languages such as Irish and Welsh, and in dialects of English, especially those that pronounce h weakly.

(Irish and Scottish Gaelic grammar) The prothesis of a t sound to words beginning with a vowel. / (Irish grammar) Replacement of an initial s sound with a t sound.