These doors are on the way out (5)
I believe the answer is:
exits
'these doors' is the definition.
The definition suggests an adverb but the answer is not.
'are on the way out' is the wordplay.
'are' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'on' is a charade indicator (letters next to each other).
'the way out' becomes 'exit' (synonyms).
's' after 'exit' is 'EXITS'.
Can you help me to learn more?
(Other definitions for exits that I've seen before include "Withdraws" , "Goes out, leaves" , "Departs" , "Leaves the stage" , "Ways out" .)