prothesis
Prothesis (noun) means the addition of phonemes to the start of a word without altering its morphological structure, for example the Spanish word esfera, derived via Latin from Greek sphaera (“sphere”); without prothesis it would have become *sfera.
Etymology
From Late Latin prothesis, prosthesis, alteration (dropping the ‘s’) from Ancient Greek πρόσθεσις (prósthesis, “addition, augmentation”), (English prosthesis) from προστίθημι (prostíthēmi, “to add”), from πρός (prós, “towards”) + τίθημι (títhēmi, “to place”), from Proto-Indo-European *próti, *préti + *dʰédʰeh₁- (“to be putting, to be placing”). However, often confused for a descendant of the Ancient Greek word πρόθεσις (próthesis, “a preposing, preposition”) (without the σ (s)), which is instead the source of a different term – see alternative etymology, below.