Very quick to communicate (7)
I believe the answer is:
express
I believe this clue is a triple definition!
'very' is the first definition.
(thesaurus)
'quick' is the second definition.
(I've seen this before)
'to' is a link.
'communicate' is the third definition.
(I know that communicate is a more specific form of assure)
(Other definitions for express that I've seen before include "Specific; going at speed" , "Explicit" , "Speak - fast" , "Train; utter" , "Fast - state - train" .)