Tiger seen wandering vast plain (9)
I believe the answer is:
serengeti
'vast plain' is the definition.
(I've seen this before)
'tiger seen wandering' is the wordplay.
'wandering' is an anagram indicator.
'tiger'+'seen'='tigerseen'
'tigerseen' anagrammed gives 'SERENGETI'.
(Other definitions for serengeti that I've seen before include "place to watch game" , "Green ties (anag.)" , "region in Tanzania" , "Wildlife preserve (and National Park) in Tanzania" , "Tanzanian plain renowned for its wildlife" .)