a person who is thoroughly experienced or exceptionally skilled in a profession, art, etc.:
a past master at chess.
a person who has held the office of master in a guild, lodge, etc.
a person with talent for, or experience in, a particular activity:
a past master of tact
a person who has held the office of master in a Freemasons' lodge, guild, etc
Collins English Dictionary - Complete & Unabridged 10th Edition
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