Note hip seams split by stress (9)
I believe the answer is:
emphasise
'stress' is the definition.
('stress'->'emphasize' is in my internal thesaurus and 'ize'->'ise')
'note hip seams split' is the wordplay.
'note' becomes 'e' (musical note).
'split' indicates anagramming the letters.
'hip'+'seams'='hipseams'
'hipseams' with letters rearranged gives 'mphasise'.
'e'+'mphasise'='EMPHASISE'
'by' acts as a link.
(Other definitions for emphasise that I've seen before include "Stress, underline" , "Mashes pie (anag.)" , "Give extra importance to" , "'Stress, accentuate (9)'" , "Place stress on" .)