Women in constituency work hard (5)
I believe the answer is:
sweat
'work hard' is the definition.
(I've seen this in another clue)
'women in constituency' is the wordplay.
'women' becomes 'w' (standard abbreviation).
'in' means one lot of letters goes inside another.
'constituency' becomes 'seat' (House of Commons seats represent constituencies).
'w' placed into 'seat' is 'SWEAT'.
(Other definitions for sweat that I've seen before include "Salty fluid secreted by glands" , "It's hard work" , "Perspire" , "Salty fluid secreted by the body" , "Toil" .)