Strain mouth? (5)
I believe the answer is:
delta
This might be a double definition.
'strain' is the first definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'mouth?' is the second definition.
(I know that delta is a type of river mouth)
Can you help me to learn more?
(Other definitions for delta that I've seen before include "sort of wing" , "Type of wing" , "Code word for D" , "Alluvial river mouth" , "Letter - where river divides" .)