Boy raised on hospital food (4)
I believe the answer is:
nosh
'food' is the definition.
(nosh is a kind of food)
'boy raised on hospital' is the wordplay.
'boy' becomes 'son' (synonyms).
'raised' says the letters should be written in reverse (going up in a down clue).
'on' means one lot of letters go next to another.
'hospital' becomes 'h' (abbreviation for hospital on maps).
'son' in reverse letter order is 'nos'.
'nos'+'h'='NOSH'
(Other definitions for nosh that I've seen before include "Food (sl.)" , "'Food, grub (4)'" , "A slang meal" , "Eats" , "Slangy food or meal" .)