Fast instructions (5)
I believe the answer is:
brief
This clue might be a double definition.
'fast' is the first definition.
(thesaurus)
'instructions' is the second definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for brief that I've seen before include "Succinct" , "Terse" , "not lasting long" , "Case given to a barrister" , "Using few words" .)