A descendent covering up king's crime (5)
I believe the answer is:
arson
'crime' is the definition.
(crime of illegally starting a fire)
'a descendent covering up king's' is the wordplay.
I cannot quite see how this works, but
'a' is within the answer.
'covering' could be 'on' and 'on' is found in the answer.
'king's' could be 'rs' (abbreviation for rex, king in Latin) and 'rs' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for arson that I've seen before include "Fire-raising crime" , "Criminal burning of property" , "Sonar (anag.)" , "Torching" , "Malicious fire-lighting" .)