Origin of frounceMiddle English frouncen ; from Old French froncir, to wrinkle ; from Frankish an unverified form hrunkja, a wrinkle, akin to Old Norse hrukka
(third-person singular simple present frounces, present participle frouncing, simple past and past participle frounced)
From Middle English frouncen, from Old French froncir "to wrinkle, frown", from Frankish *hrunkja "a wrinkle" from Proto-Germanic *hrunkijō, *hrunkitō (“fold, wrinkle”), from Proto-Indo-European *(s)ker- (“to turn, bend”). Akin to Old High German runza "fold, wrinkle, crease" (German Runzel "wrinkle"), Middle Dutch ronse "frown", Old Norse hrukka "wrinkle, crease" (Icelandic hrukka "wrinkle, crease, ruck"). More at ruck2.