OK for audio (5)
I believe the answer is:
sound
This could be a double definition.
'ok for' is the first definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'audio' is the second definition.
(synonyms)
Can you help me to learn more?
(Other definitions for sound that I've seen before include "to do the plumbing?" , "Ocean inlet or deep bay" , "Healthy; narrow channel" , "Fit" , "Valid" .)