Hoary source of some merriment (4)
I believe the answer is:
rime
'hoary source' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'some merriment' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'RIME' can be found hidden inside 'merriment'.
'of' is the link.
Can you help me to learn more?
(Other definitions for rime that I've seen before include "dated poetry" , "Ice" , "Type of frost" , "''The ... of the Ancient Mariner'' (Coleridge)" , "Kind of frost in mire" .)