measles (n.)
infectious disease, early 14c., plural of Middle English masel, perhaps from Middle Dutch masel "blemish" (in plural "measles") or Middle Low German masele, from Proto-Germanic *mas- "spot, blemish" (cognates: Old High German masla "blood-blister," German Masern "measles").

There might have been an Old English cognate, but if so it has not been recorded. Form probably influenced by Middle English mesel "leprous" (late 13c.).