Mournful chap supporting scheme (8)
I believe the answer is:
plangent
'mournful' is the definition.
(thesaurus)
'chap supporting scheme' is the wordplay.
'chap' becomes 'gent' (I've seen this in other clues**).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'scheme' becomes 'plan' (I've seen this before).
'gent' after 'plan' is 'PLANGENT'.
(Other definitions for plangent that I've seen before include "Loud and sad" , "Clangorous" , "Resonant, reverberating with mournful sound" , "Resounding" , "(Of sound) mournfully resonant" .)