An Etymological Dictionary of the German Language/Annotated/Mütze

Mütze, feminine, from the equivalent late Middle High German mütze, mutze, feminine, ‘cap, bonnet,’ which is a shortened form of the equivalent armuȥ, almuȥ. It is derived from Middle Latin almutia, armutia, almutium, properly ‘amictus quo Canonici caput humerosque tegebant,’ worn also at a later period by laymen; the development of meaning is similar to that of Modern High German Kappe. Middle Latin almutia, the origin of which is entirely obscure (al is thought to be the Arabic article), appears in Romance. Compare French aumusse or aumuce, ‘amess’ (fur cap worn by officials in Roman Catholic churches).