Fashionable notes used in chants (7)
I believe the answer is:
intones
'chants' is the definition.
('intone' can be a synonym of 'chant')
'fashionable notes used in' is the wordplay.
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'used' indicates an anagram.
'in' indicates putting letters inside.
'notes' anagrammed gives 'tones'.
'in' inserted within 'tones' is 'INTONES'.
(Other definitions for intones that I've seen before include "Chants" , "Recites in a chanting voice" .)