Weak female leaves bar (4)
I believe the answer is:
rail
'bar' is the definition.
(I know that rail is a type of bar)
'weak female leaves' is the wordplay.
'weak' becomes 'frail' (similar in meaning).
'female' becomes 'f' (abbreviation).
'leaves' suggests deleting specific letters.
'frail' with 'f' removed is 'RAIL'.
(Other definitions for rail that I've seen before include "transport system" , "Kind of transport" , "Track - complain - bird" , "Bar of rolled steel" , "Bar; waterside bird" .)