past master
noun
1
- a person who is particularly skilled at a specified activity or art行家, 能手：
he's a past master at keeping his whereabouts secret.
他非常善于隐瞒自己的行踪。
2
- a person who has held the position of master in an organization前会长, 前主席：
he was a past master of the City Company of Grocers.
他是市百货公司的前董事长。