Details of his pectorals (4)
I believe the answer is:
spec
'details' is the definition.
The answer and definition 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?
'of his pectorals' is the wordplay.
'of' indicates a hidden word.
'SPEC' is hidden in the letters of 'his pectorals'.
Can you help me to learn more?
(Other definitions for spec that I've seen before include "Estimate" , "Gamble (colloq.)" , "Instructions" , "Bet" , "Detailed design document (abbr.)" .)