mess about

phrasal verb

messed about; messing about; messes about

Definition of mess about

British, informal

1 : to spend time doing things that are not useful or serious : to waste time We just messed about all afternoon. She spent the evening messing about on the computer. It's time we stopped messing about and got busy.

2 : to have sex with someone who is not one's husband, wife, or regular partner His wife discovered that he was messing about (on her). —often + with His wife discovered that he was messing about with his secretary.