Lad raised on hospital grub (4)
I believe the answer is:
nosh
'grub' is the definition.
(I've seen this before)
'lad raised on hospital' is the wordplay.
'lad' becomes 'son' (lad can informally mean a young boy).
'raised' says the letters should be written in reverse (going up in a down clue).
'on' is a charade indicator (letters next to each other).
'hospital' becomes 'H' (abbreviation for hospital on maps).
'son' reversed gives 'nos'.
'nos'+'h'='NOSH'
(Other definitions for nosh that I've seen before include "Food - eat greedily" , "eating this?" , "Eat (sl.)" , "cuisine" , "chow" .)