A misnomer is a name that is incorrectly or unsuitably applied. Misnomers often arise because something was named long before its correct nature was known, or because an earlier form of something has been replaced by a later form to which the name no longer suitably applies. A misnomer may also be a word that is used incorrectly or misleadingly. The word "misnomer" does not mean "misunderstanding" or "popular misconception", and a number of misnomers remain in common usage — which is to say that a word being a misnomer does not necessarily make usage of the word incorrect.

The term anachronym refers to this type of misnomer. "Anachronym" should not be confused with anacronyms, which refers to words (such as laser, sonar and scuba) with acronymic origin but which are now used syntactically as words in their own right.