a type of woman's indoor cap, 1795 (as simply mob, 1748), from obs. mob "a strumpet" (earlier mab, 1557) + cap. The first element is related to obs. verb mob "to tousle the hair, to dress untidily" (1664), and perhaps ult. from mop but infl. by Mab
as a fem. name. Du. has a similar compound, mopmuts, but the relationship between it and the Eng. word is uncertain.