Boy repulsed by hospital food (4)
I believe the answer is:
nosh
'food' is the definition.
(nosh is a kind of food)
'boy repulsed by hospital' is the wordplay.
'boy' becomes 'son' ('son' can be a synonym of 'boy'**).
'repulsed' says the letters should be written backwards.
'by' is a charade indicator (letters next to each other).
'hospital' becomes 'h'.
'son' written backwards gives 'nos'.
'nos'+'h'='NOSH'
(Other definitions for nosh that I've seen before include "cuisine" , "chow" , "A slang meal" , "Eat (sl.)" , "(Eat) a snack" .)