One going round hospital in pain (4)
I believe the answer is:
ache
'pain' is the definition.
(ache is a kind of pain)
'one going round hospital' is the wordplay.
'one' becomes 'ace' ('ace' can be a synonym of 'one').
'going round' is an insertion indicator.
'hospital' becomes 'h'.
'ace' going around 'h' is 'ACHE'.
'in' acts as a link.
(Other definitions for ache that I've seen before include "agony" , "Dull steady pain" , "Feel sore" , "Each (anag.)" , "suffering" .)