Communicate fast (7)
I believe the answer is:
express
This clue is a double definition.
'communicate' is the first definition.
(I know that communicate is a more specific form of the action covenant)
'fast' is the second definition.
(I've seen this before)
(Other definitions for express that I've seen before include "Utter; without stopping" , "Non-stop(ping)" , "Fast train; specific" , "Convey; particular; train" , "for a specific purpose?" .)