Function like a group of politicians (5)
I believe the answer is:
party
'a group of politicians' is the definition.
(political party)
'function like' is the wordplay.
'function' becomes 'part' (synonyms).
'like' becomes 'y' (similar in meaning).
'part'+'y'='PARTY'
(Other definitions for party that I've seen before include "Group gathered together for pleasure" , "Social function" , "Social occasion - political group" , "Celebratory social gathering" , "Crew" .)