"inflammation on a finger or toe," mid-15c., alteration of whitflaw (c. 1400), from flaw, with first element possibly from Dutch vijt or Low German fit "abscess."
Entries linking to whitlow
flaw n.
early 14c., "a flake" (of snow), also in Middle English "a spark of fire; a splinter," from Old Norse flaga "stone slab, layer of stone" (see flag (n.2)), perhaps used here in an extended sense. Old English had floh stanes, but the Middle English form suggests a Scandinavian origin. "The close resemblance in sense between flaw and flake is noteworthy" [OED]. Sense of "defect, fault" first recorded 1580s, first of character, later (c. 1600) of material things; probably via notion of a "fragment" broken off.