From the monarch, a sign of willingness (5)
I believe the answer is:
offer
'a sign of willingness' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'from the monarch' is the wordplay.
'from' becomes 'off' (I've seen this in other clues).
'the monarch' becomes 'ER' (abbreviation for Elizabeth Regina, British Queen).
'off'+'er'='OFFER'
Can you help me to learn more?
(Other definitions for offer that I've seen before include "Volunteer, present" , "Present to or make a bid" , "Tender or propose" , "Volunteer -- proposal" , "killer?" .)