mob cap
Concise Oxford English Dictionary © 2008 Oxford University Press:
mob cap
▶noun a large, soft indoor hat covering the hair, worn by women in the 18th and early 19th centuries.
– origin C18 (orig. in the sense ‘prostitute’, later ‘négligé’): mob, var. of obs. mab ‘slut’.
'mob cap' also found in these Oxford entries:

