Male legislator weed (4)
I believe the answer is:
hemp
'weed' is the definition.
(thesaurus)
'male legislator' is the wordplay.
'male' becomes 'he' (he refers to a man).
'legislator' becomes 'MP' (an MP legislates in parliament).
'he'+'mp'='HEMP'
(Other definitions for hemp that I've seen before include "Grass" , "Rope-making fibre" , "Rope, cannabis, plant" , "tea" , "Plant for rope or pot" .)