Epenthesis is the addition of a vowel or consonant sound to a word. This is applied differently to different languages, and works in various ways according to the needs of a set of speakers. The word comes from the Greek, where it could be translated into English as, "put into."

In many cases, epenthesis happens because speakers find it hard to pronounce vowel or consonant clusters, or sets of combined vowels and consonants, that are next to each other in words. Experts sometimes describe these ways of speaking as "child-like," where a given dialect inserts the sounds to make speech easier.

The use of epenthesis in dialect is a major part of understanding how this phenomenon happens; speakers frequently add sounds into words in ways that are not technically correct, but become common usage over time, at least in specific language communities. The use of these extra sounds can also enhance a poetic meter.

One common example of epenthesis in English helps to describe how this process works. English speakers may use a "stopping" consonant as a kind of accent, in ways that are entirely superfluous. For example, inserting a "p" sound into a word like "hamster" or even a word like "teamster" gives the word a slightly different sound, but does not change its meaning or add substance.