This document defines and provides examples of epenthesis, which is the insertion of an extra sound into a word. Epenthesis can occur historically as languages evolve over time, such as the addition of 't' in French interrogatives. It can also occur synchronically as a rule in the language's phonology. Epenthesis arises for reasons like making consonant clusters or vowels in hiatus easier to pronounce. It is divided into excrescence, the addition of a consonant, and anaptyxis, the addition of a vowel. Epenthesis is a feature of both spoken language and can occur as a poetic device.