Omen left by hospital department (7)
I believe the answer is:
portent
'omen' is the definition.
(I know that omen can be written as portent)
'left by hospital department' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'by' means one lot of letters go next to another.
'hospital department' becomes 'ENT' (abbreviation for Ear, Nose and Throat department).
'port'+'ent'='PORTENT'
(Other definitions for portent that I've seen before include "Prophetic sign" , "Sign of thing to come" , "Evil omen" , "bad sign" , "Sign of something about to happen" .)