From Middle English pleck, plek, perhaps a variation of plack, or perhaps from Middle Dutch plecke, ultimately from Proto-West Germanic *plakkju, from Proto-Germanic *plakjō (“spot, stain”).
Cognate with West Frisian plak (“place, location, spot”), Dutch plek (“place, spot, patch”), Low German Plakk, Plakke (“spot, place, patch”). More at patch.