Segregation is new to a lion (9)
I believe the answer is:
isolation
'segregation' is the definition.
(thesaurus)
'is new to a lion' is the wordplay.
'new' indicates anagramming the letters.
'to'+'a'+'lion'='toalion'
'toalion' is an anagram of 'olation'.
'is'+'olation'='ISOLATION'
(Other definitions for isolation that I've seen before include "Separation - solitude" , "Cutting off" , "State of separation, closing off" , "Detachment" , "Staff in such a hospital working with" .)