Constituency wife held for Labour (5)
I believe the answer is:
sweat
'labour' is the definition.
(sweat is a kind of labour)
'constituency wife held' is the wordplay.
'constituency' becomes 'seat' (I've seen this before).
'wife' becomes 'w'.
'held' means one lot of letters goes inside another.
'seat' going around 'w' is 'SWEAT'.
'for' is the link.
(Other definitions for sweat that I've seen before include "Waste (anag.)" , "Salty fluid secreted by glands" , "Perspire" , "Male perspiration?" , "Toil" .)