Fancy man in particular supporting wife (4)
I believe the answer is:
whim
'fancy' is the definition.
(I've seen this before)
'man in particular supporting wife' is the wordplay.
'man in particular' becomes 'him' ('him' can be used to indicate a particular man).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'wife' becomes 'w'.
'him' put after 'w' is 'WHIM'.
(Other definitions for whim that I've seen before include "Caprice, sudden fancy" , "Fanciful impulse" , "Fanciful idea" , "'Caprice, notion (4)'" , "Passing fancy" .)