Detective, glum, missing second round (5)
I believe the answer is:
morse
This could be a double definition.
'detective' is the first definition.
(Inspector Morse, fictional detective)
'glum missing second round' is the second definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for morse that I've seen before include "used to transmit messages" , "& 24 Across Encrypted language" , "Colin Dexter's fictional detective" , "Radio code inventor" , "Dot-dash code inventor" .)