Cleaner's vehicle outside hospital (4)
I believe the answer is:
char
'cleaner's' is the definition.
(I've seen this before)
'vehicle outside hospital' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle**).
'outside' means one lot of letters goes inside another.
'hospital' becomes 'h'.
'car' placed around 'h' is 'CHAR'.
(Other definitions for char that I've seen before include "Daily cleaner; burn" , "way to make carbon" , "Make black by burning, or a small trout" , "Singe, scorch" , "Kind of small trout - burn it black" .)