Boast about monarch dropping name (4)
I believe the answer is:
crow
'boast about' is the definition.
(I've seen this before)
'monarch dropping name' is the wordplay.
'monarch' becomes 'CR' (short for Carolus Rex, King Charles in Latin).
'dropping name' becomes 'ow' (I can't justify this - if you can you should give a lot more credence to this answer).
'cr'+'ow'='CROW'
Can you help me to learn more?
(Other definitions for crow that I've seen before include "one often getting stoned!" , "One commonly stoned" , "One joins others in a murder" , "Blow one's own trumpet" , "Express gleeful triumph" .)