Pain from ailment could hurt, even initially (4)
I believe the answer is:
ache
'pain' is the definition.
(ache is a kind of pain)
'ailment could hurt even initially' is the wordplay.
'initially' says to take the initial letters.
The first letters of 'ailment could hurt even' is 'ACHE'.
'from' is the link.
(Other definitions for ache that I've seen before include "Dull throbbing pain" , "A dull lingering pain" , "Throb - hurt" , "Dull prolonged pain" , "anguish" .)