Hurt expert rings hospital (4)
I believe the answer is:
ache
'hurt' is the definition.
(synonyms)
'expert rings hospital' is the wordplay.
'expert' becomes 'ace' (ace can informally mean very good).
'rings' means one lot of letters goes inside another (some letters are ringed or contained by others).
'hospital' becomes 'h' (abbreviation for hospital on maps).
'ace' enclosing 'h' is 'ACHE'.
(Other definitions for ache that I've seen before include "Feel sore" , "Play up" , "Hanker" , "Dull prolonged pain" , "Pine" .)