Stay fit to support daughter (5)
I believe the answer is:
dwell
'stay' is the definition.
(I've seen this before)
'fit to support daughter' is the wordplay.
'fit' becomes 'well' ('well' is associated in meaning with 'fit').
'to support' is a charade indicator (letters next to each other) (in a down clue, some letters hold others up).
'daughter' becomes 'd'.
'well' put after 'd' is 'DWELL'.
(Other definitions for dwell that I've seen before include "Reside - linger" , "Live (in a place)" , "Abide, reside" , "Inhabit" , "Exist (within)" .)