Person from mountainous territory: Alpine ground (6)
I believe the answer is:
nepali
'person from mountainous territory' is the 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?
'alpine ground' is the wordplay.
'ground' is an anagram indicator ('grind' the letters into a new form).
'alpine' with letters rearranged gives 'NEPALI'.
Can you help me to learn more?
(Other definitions for nepali that I've seen before include "Asian national" , "One from Katmandu" , "Language of Kathmandu" , "Native of one Himalayan state" , "Foreigner" .)