Similar meaning, more formal:
* Solecism: This refers to a grammatical error, but can also be used to describe a misuse of words.
* Misusage: A general term for using a word incorrectly.
* Mispronunciation: If the error specifically relates to the pronunciation of a word.
* Verbal faux pas: A general term for a verbal mistake that is considered embarrassing or humorous.
Informal and humorous:
* Spoonerism: This refers to a specific type of malapropism where the initial sounds of two words are switched (e.g., "a blushing crow" instead of "a crushing blow").
* Word salad: This is a more general term for nonsensical speech that is often used to describe the speech of someone with dementia or other cognitive impairment.
The best synonym to use will depend on the specific situation and the level of formality you want to achieve.