mm abbreviation

Universal Words , exclamation abbreviation MILLIMETRE(S): rainfall 6mm * a 35mm camera exclamation (also mmm) the way of writing the sound that people make to show that they are listening to sb or that they agree, they are thinking, they like sth, they are not sure, etc: Mm, I know what you mean. * Mm, what lovely cake! * Mmm, I'm not so sure that's a good idea.