Measure big cheese (5)
I believe the answer is:
ruler
This could be a double definition.
'measure' is the first definition.
(ruler is a kind of measure)
'big cheese' is the second definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I can't see?
Can you help me to learn more?
(Other definitions for ruler that I've seen before include "Queen, say" , "Queen, perhaps" , "One measures" , "Monarch - drafting tool" , "One governing" .)