The origin of the phrase past master is uncertain, though it may be related to Masonic nomenclature. We will examine the definition of the term past master, where it may have come from and some examples of its use in sentences.
A past master is someone who is an expert at something due to his long involvement and practice in that thing. The term past master originally referred to someone who had served in a post as the master of something, and no longer served in that capacity. Most often, the term past master was used to denote a man who had once served as the master of a Freemason lodge but no longer served in that capacity. In time, the term past master evolved to mean someone who is an expert due to his long involvement with something. Note that the word past is an adjective, not the verb form passed. Further, note that past master is two words. The plural form of past master is past masters.
Examples
The man has mystical influence with the Legislature (see above, the Mario M. Cuomo Bridge); the official state watchdog, Comptroller Tom DiNapoli, is terrified of him; he carries the state Thruway Authority, which owns both bridges, in his cargo shorts — and he’s a past master at co-opting private-sector interest groups. (The New York Post)
He later was a member of the New England Telephone Pioneers of America, past master of Oriental Star Lodge AF & AM of Livermore, past commander of the State VFW and past commander of Frank L. Mitchell VFW Post 3335 in Jay, and the George Bunton American Legion Post 10 in Livermore Falls. (The Sun Journal)