Not tame
'not tame' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for feral that I've seen before include "'Savage, wild (5)'" , "Flare up in wild state" , "Fierce, having reverted to wild state" , "Escaped-into-wild (animal)" , "Wild or brutal" .)
'not tame' is the definition.
('wild' is the opposite to 'tame')
This is all the clue.
(Other definitions for wild that I've seen before include "Not tamed" , "Unrestrained" , "Impulsive" , "Undomesticated" , "Feral, untamed" .)