Note inclination is a pain (5)
I believe the answer is:
cramp
'pain' is the definition.
(I have seen 'Muscular pain' mean 'cramp' so perhaps 'pain' could also mean 'cramp')
'note inclination' is the wordplay.
'note' becomes 'c' (musical note).
'inclination' becomes 'ramp' (an inclined surface).
'c'+'ramp'='CRAMP'
'is a' acts as a link.
(Other definitions for cramp that I've seen before include "hamper" , "Muscular spasm, very painful" , "Painful muscle problem" , "Severe muscular pain" , "Sudden painful tightening of a muscle" .)