Question authority (3)
I believe the answer is:
who
This clue is a double definition.
'question' is the first definition.
(I've seen this before)
'authority' is the second definition.
(WHO is an example)
(Other definitions for who that I've seen before include "Question of identity" , "Universal health body" , "Alien doctor" , "Which people" , "Time-travelling Doctor" .)