Naked scoundrel at last donning pants (4)
I believe the answer is:
bald
'naked' is the definition.
(thesaurus)
'scoundrel at last donning pants' is the wordplay.
'at last' says to take the final letters.
'donning' indicates putting letters inside (I've seen this in other clues).
'pants' becomes 'bad' (British slang - it was pants).
The final letter of 'scoundrel' is 'l'.
'l' inserted within 'bad' is 'BALD'.
(Other definitions for bald that I've seen before include "Without hair" , "Plain; hairless" , "Unadorned" , "Without the natural covering" , "With no effort to conceal" .)