noun
Etymology: past (I) + master
1. : one who has held the office of worshipful master in a lodge of Freemasons or of master in a guild, club, or other society
2.
[alteration (influenced by past ) (I) of passed master ]
: one who is expert in some art, subject, or activity : a thorough master : adept
a past master at exploiting differences among his opposition — W.G.Hardy