Czech gents thus clothed (6)
I believe the answer is:
slavic
'czech' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'gents thus clothed' is the wordplay.
I cannot quite understand how this works, but
'gents' could be 'lav' (gents toilet or lavatory) and 'lav' is present in the answer.
'thus' could be 'sic' ('thus' in Latin) and 'sic' is located in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for slavic that I've seen before include "Relating to a race of Eastern Europeans" , "From eastern Europe" .)