Pain expert nursing Henry (4)
I believe the answer is:
ache
'pain' is the definition.
(ache is a kind of pain)
'expert nursing henry' is the wordplay.
'expert' becomes 'ace' (ace can informally mean very good).
'nursing' indicates putting letters inside.
'henry' becomes 'H' (symbol for the unit of electrical inductance).
'ace' going around 'h' is 'ACHE'.
(Other definitions for ache that I've seen before include "Hanker" , "A dull lingering pain" , "Each (anag.)" , "Feel sore" , "painful" .)