Stout king in his den (6)
I believe the answer is:
sturdy
'stout' is the definition.
(I know that stout can be written as sturdy)
'king in his den' is the wordplay.
I cannot really understand how this works, but
'king' could be 'r' (abbreviation for rex, king in Latin) and 'r' is found in the answer.
'den' could be 'study' (I've seen this in another clue) and 'study' is present in the remaining letters.
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 sturdy that I've seen before include "Strong and stout" , "Strong and sturdily built" , "Rugged" , "Stout, brawny" , "Firmly constructed" .)