Brown rejected name associated with mountains — genuine (7)
I believe the answer is:
natural
'genuine' is the definition.
(thesaurus)
'brown rejected name associated with mountains' is the wordplay.
'brown rejected name' becomes 'nat' (I am not sure about this - if you are sure you should believe this answer much more).
'associated with' says to put letters next to each other.
'mountains' becomes 'ural' (the Ural Mountains).
'nat'+'ural'='NATURAL'
Can you help me to learn more?
(Other definitions for natural that I've seen before include "Reason for death when not suspicious" , "Unvarnished" , "(In music) neither sharp nor flat" , "Normal - innate - instinctive" , "An ideal person" .)