Word that describes a den that's black inside, cold inside (9)
I believe the answer is:
adjective
'word that describes' is the definition.
(adjectives are descriptive words)
'a den that's black inside cold inside' is the wordplay.
I cannot quite understand how this works, but
'a' is found in the answer.
'cold' could be 'c' (eg on taps) and 'c' is located in the answer.
'black' could be 'jet' (similar in meaning) and 'jet' is found within the remaining letters.
'den' could be 'dive' (both can mean a hideout) and 'dive' is found within the remaining letters.
No letters remain.
This explanation may well be incorrect...
(Other definitions for adjective that I've seen before include "Word qualifying a noun" , "Descriptive word" , "It describes a noun" , "Word added to noun to qualify meaning" , "Word describing" .)