Trio cease performing - they're largely unknown (9)
I believe the answer is:
esoterica
'largely unknown' 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?
'trio cease performing' is the wordplay.
'performing' indicates anagramming the letters.
'trio'+'cease'='triocease'
'triocease' anagrammed gives 'ESOTERICA'.
'they're' acts as a link.
Can you help me to learn more?
(Other definitions for esoterica that I've seen before include "collection of specialist stuff" , "secrets to a few" , "Highly specialised subjects" , "things not seen by many?" , "Coarse tie? (anag)" .)