Tactless, corpulent monarch? (10)
I believe the answer is:
unthinking
'tactless' is the definition.
(thesaurus)
'corpulent monarch?' is the wordplay.
I cannot quite see how this works, but
'monarch?' could be 'king' (king is a kind of monarch) and 'king' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for unthinking that I've seen before include "Knee-jerk" , "inconsiderate" .)