He's so wrong to go by car! (5)
I believe the answer is:
oscar
'he's' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'so wrong to go by car' is the wordplay.
'wrong' indicates anagramming the letters.
'to go by' means one lot of letters go next to another.
'so' with letters rearranged gives 'os'.
'os'+'car'='OSCAR'
Can you help me to learn more?
(Other definitions for oscar that I've seen before include "-- Wilde, author" , "letter read out on radio" , "The familiar Mr Wilde, playwright" , "Develop again" , "Film industry award" .)