Mistake to suppress note in horn (5)
I believe the answer is:
siren
'horn' is the definition.
(thesaurus)
'mistake to suppress note' is the wordplay.
'mistake' becomes 'sin'.
'to suppress' is an insertion indicator.
'note' becomes 're' (as in do-re-mi).
'sin' placed around 're' is 'SIREN'.
'in' is the link.
(Other definitions for siren that I've seen before include "Loud whistle or sailors' enchantress" , "Dangerously fascinating woman" , "Loud whistle or dangerous woman" , "Seductive woman" , "Warning sound" .)