epenthesis

The insertion of a phoneme, letter, or syllable into a word, usually to satisfy the phonological constraints of a language or poetic context.

Pronounced as (IPA)

/ɪˈpɛn.θə.sɪs/

Middle of 16th century: via Late Latin, from Ancient Greek ἐπένθεσις (epénthesis), from ἐπεντίθημι (epentíthēmi, “I insert”), from ἐπί (epí) + ἐντίθημι (entíthēmi, “I put in”), from ἐν (en, “in”) + τίθημι (títhēmi, “I put, place”).