Measure of authority (4)
I believe the answer is:
rule
This clue is a double definition.
'measure' is the first definition.
(I know that rule is a type of measure)
'authority' is the second definition.
(I've seen this in another clue)
'of' is the link.
(Other definitions for rule that I've seen before include "Lure with regulation" , "Control using lure." , "Control; printed line" , "Strip" , "Determination" .)