Fancy the man supporting wife (4)
I believe the answer is:
whim
'fancy' is the definition.
(I've seen this before)
'the man supporting wife' is the wordplay.
'the man' becomes 'him' ().
'supporting' means one lot of letters go next to another (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 "Sudden odd desire" , "Fad" , "Urge" , "Impulse or caprice" , "fantastic creation from the past" .)