A tie is an accessory (10)
I believe the answer is:
attachment
I believe this is a double definition.
'a tie' is the first definition.
(thesaurus)
'an accessory' is the second definition.
(thesaurus)
'is' acts as a link.
(Other definitions for attachment that I've seen before include "Affinity" , "File with an email" , "communicated via e-mail" , "devotion" , "what might accompany 50 [EMAIL]" .)