of a piece

From an obsolete sense of a (“the same”).

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of a piece

1. (idiomatic) Of the same kind.

   Synonyms: of a kind, of a blood, of a feather

   Near-synonyms: all one, all the same, cut from the same cloth, of the same stripe, monolithic

   • 1894, James George Frazer, The Golden Bough‎^[1]:

     Strange as this expectation appears to us, it is quite of a piece with early modes of thought.

   • 1980, AA Book of British Villages, Drive Publications Ltd, page 375, about Terling:

     Further along, the road passes a low E-shape of red-brick estate buildings, obviously modern, yet all of a piece with this sensible, attractive and businesslike village.

2. Used other than figuratively or idiomatically: see of,‎ a,‎ piece.

• of a piece with