Boy brought up hospital food (4)
I believe the answer is:
nosh
'food' is the definition.
(nosh is a kind of food)
'boy brought up hospital' is the wordplay.
'boy' becomes 'son' (synonyms).
'brought up' shows that the letters should be reversed in order (in a down clue, letters go up).
'hospital' becomes 'H' (abbreviation for hospital on maps).
'son' back-to-front is 'nos'.
'nos'+'h'='NOSH'
(Other definitions for nosh that I've seen before include "Slangy food or meal" , "chow" , "Food (Yiddish)" , "'Food, grub (4)'" , "Scoff" .)