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early 14c., "a flake" (of snow), also in Middle English "a spark of fire; a splinter," from Old Norse flaga "stone slab, flake" (see flagstone); sense of "defect, fault" first recorded 1580s, first of character, later (c.1600) of material things; probably via notion of a "fragment" broken off.
early 15c. (implied in flawed); see flaw (n.). Related: Flawing.