Room key (5)
I believe the answer is:
space
This could be a double definition.
'room' is the first definition.
(I've seen this before)
'key' is the second definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I can't see?
Can you help me to learn more?
(Other definitions for space that I've seen before include "Gap between words" , "Gap; --- Oddity (Bowie)" , "Empty area, may be outer" , "Room for capes" , "Free area" .)