Topless dress? Rather! (1,3)
I believe the answer is:
a bit
'rather' is the definition.
(I've seen this before)
'topless dress?' is the wordplay.
'topless' means to remove the first letter.
'dress?' becomes 'habit' (habiting is a kind of dressing).
'habit' with its initial letter taken away is 'A BIT'.
(Other definitions for a bit that I've seen before include "Somewhat" , "Rather" , "to some extent" , "Slightly" , "fairly?" .)