infectious disease causing eruptions of rose-colored papulae, early 14c., plural of Middle English masel "little spot," which is perhaps from Middle Dutch masel "blemish" (in plural "measles") or Middle Low German masele, both from Proto-Germanic *mas- "spot, blemish" (source also of 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. "The phonetic development is irregular" [OED] and the form might have been influenced by Middle English mēsel "leprous; a leper; leprosy" (late 13c., obsolete from mid-16c.), which is from Old French mesel and directly from Medieval Latin misellus "a wretch," noun use of an adjective meaning "wretched," a diminutive of Latin miser "unhappy, wretched, pitiable, in distress."
"leprous" (adj.); "a leper" (n.); both c. 1300, from Old French mesel "wretched, leprous; a wretch," from Latin misellus "wretched, unfortunate," as a noun, "a wretch," in Medieval Latin, "a leper," diminutive of miser "wretched, unfortunate, miserable" (see miser). A Latin diminutive form without diminutive force. Also from Latin misellus are Old Italian misello "sick, leprous," Catalan mesell "sick." The English word is archaic or obsolete since the 1500s, replaced by leper, leprous, but its lexical DNA survives, apparently, as a contamination of measles.
"German measles," contagious disease characterized by rose-colored eruptions, 1883, Modern Latin, literally "rash," from noun use of neuter plural of Latin rubellus "reddish," diminutive of ruber "red" (from PIE root *reudh- "red, ruddy.").
plural petechiae, "small crimson or purple spots on skin," c. 1795 (from 1580s in English texts as an Italian word), Modern Latin, from Italian petecchia "specks or freckles on the face," in plural form petecchie "measles," a word of unknown origin. Related: Petechial.