Originally living under tree, like a wolf (6)
I believe the answer is:
lupine
'like a wolf' is the definition.
(I've seen this before)
'originally living under tree' is the wordplay.
'originally' suggests taking the first letters.
'tree' becomes 'pine' (pine is a kind of tree).
The first letters of 'living under' is 'lu'.
'lu'+'pine'='LUPINE'
(Other definitions for lupine that I've seen before include "Wolfish" , "Like a wolf" , "Wolflike" , "Like some ferocious beast" , "Of or like wolves" .)