Food from hospital lad rejected (4)
I believe the answer is:
nosh
'food' is the definition.
(nosh is a kind of food)
'hospital lad rejected' is the wordplay.
'hospital' becomes 'h'.
'lad' becomes 'son'.
'rejected' shows that the letters should be reversed in order.
'h'+'son'='hson'
'hson' written backwards gives 'NOSH'.
'from' acts as a link.
(Other definitions for nosh that I've seen before include "A slang meal" , "Food (coll)" , "Food - eat greedily" , "Eats" , "Fare" .)