Jack finds one to be a sneer (4)
I believe the answer is:
jibe
'a sneer' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'jack finds one to be' is the wordplay.
'jack' becomes 'j' (playing card abbreviation).
'finds' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'j'+'i'+'be'='JIBE'
Can you help me to learn more?
(Other definitions for jibe that I've seen before include "Barb" , "Mock; jeer" , "Mocking remark" , "Scoff" , "provocation" .)