It may cause you to swallow your words (4,2,3,6)
I believe the answer is:
slip of the tongue
'words' is the definition.
The answer and definition 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?
'it may cause you to swallow your' is the wordplay.
I cannot really understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
'cause' could be 'slip' (slip is a kind of cause) and 'slip' is located in the answer.
'you' could be 'u' (commonly used in online communication) and 'u' is located in the answer.
'to' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for slip of the tongue that I've seen before include "Error in words" , "mistake one hears" , "a small error" , "vocal error" .)