to talk about sth; to mean sth; to talk in a boring or complaining way about sth
be on about sth
to talk about sth; to mean sth
I didn't know what he was on about. It didn't make sense.
be / go / keep on about sthdespectivo
to talk in a boring or complaining way about sth
Stop keeping on about it!
Definiciones del Oxford Advanced Learner's Dictionary, 9.ª edición