eggcorn

An eggcorn is the alteration of a word or phrase through the mishearing or reinterpretation of one or more of its elements, creating a new phrase that is plausible when used in the same context.

The term (originally egg corn) was coined in response to an article by Mark Liberman on the website Language Log. The article discussed the case of a woman who had used the phrase egg corn for acorn, and noted that this type of substitution lacked a name. Pullum suggested using egg corn as a label.