Agreement since transmitted (6)
I believe the answer is:
assent
'agreement' is the definition.
(I know that assent is a type of agreement)
'since transmitted' is the wordplay.
'since' becomes 'as' (both can mean 'because').
'transmitted' becomes 'sent' ('send' can be a synonym of 'transmit').
'as'+'sent'='ASSENT'
(Other definitions for assent that I've seen before include "Acquiesce, comply" , "Permission" , "Agree - concede" , "Say yes" , "Expression of agreement" .)