Stop having new nationality (7)
I believe the answer is:
finnish
'nationality' is the definition.
(from the nation of Finland)
'stop having new' is the wordplay.
I cannot quite understand how this works, but
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is present in the answer.
'stop' could be 'finish' (synonyms) and 'finish' is located in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for finnish that I've seen before include "Nationality of citizens of Helsinki" , "race" , "European language" , "Eg, native to Helsinki" , "foreign language" .)