A large tree growing in a mountainous region (6)
I believe the answer is:
alpine
'growing in a mountainous region' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
'a large tree' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'tree' becomes 'pine' (pine tree is a kind of tree).
'a'+'l'+'pine'='ALPINE'
Can you help me to learn more?
(Other definitions for alpine that I've seen before include "To do with great European mountains" , "Native growing up in mountainous area" , "Relating to a European mountain range" , "seen in rocky state?" , "Plant of high mountains" .)