a person who is thoroughly experienced or exceptionally skilled in a profession, art, etc.:
a past master at chess.
2.
a person who has held the office of master in a guild, lodge, etc.
Origin
1755-65
British Dictionary definitions for past master
past master
noun
1.
a person with talent for, or experience in, a particular activity: a past master of tact
2.
a person who has held the office of master in a Freemasons' lodge, guild, etc
Idioms and Phrases with past master
past master
A person who is thoroughly experienced or exceptionally skilled in some activity or craft. For example, We're lucky to get Ella, because she's a past master at fundraising. This expression probably alludes to the original literal meaning, that is, one who formerly held the post of master in a lodge or other organization. Although past mistress was used for an exceptionally skilled woman in the mid-1800s, it is heard less often today, master serving for both sexes. [ Mid-1800s ]