From Longman Dictionary of Contemporary Englishbe a past master (at something)be a past master (at something)British EnglishGOOD AT to be very good at doing something because you have done it a lot He’s a past master at getting free drinks out of people. → master
Examples from the Corpus
be a past master (at something)• Johnny Morris is a past master at both.• That sort of thing wasn't her style at all, but Susan was a past master at it. 