Indoor hat (6)
I believe the answer is:
mobcap
'indoor hat' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for mobcap that I've seen before include "headgear" , "18th-century woman's indoor hat" , "Former hat for women" , "old hat" , "C 18 - nineteen women's large soft indoor hat" .)