Key for ward (5)
I believe the answer is:
minor
This clue is a double definition.
'key' is the first definition.
(thesaurus)
'ward' is the second definition.
(thesaurus)
'for' acts as a link.
(Other definitions for minor that I've seen before include "Like clubs" , "Insignificant" , "Young person below voting age" , "Unimportant or unable to vote" , "Secondary" .)