Initially acting like a monarch, we hear, can be trying (10)
I believe the answer is:
arraigning
'be trying' is the definition.
(to arraign someone is to bring them to trial)
'initially acting like a monarch we hear' is the wordplay.
'initially' indicates taking the first letters.
'like a monarch' becomes 'reigning' (monarchs reign).
'we hear' shows a homophone (sound like).
The initial letter of 'acting' is 'a'.
'reigning' sounds like 'rraigning'.
'a'+'rraigning'='ARRAIGNING'
'can' is the link.
(Other definitions for arraigning that I've seen before include "Calling before a court to answer charge" , "putting in front of bench" .)