Old woman, smarter, is fearsome creature (8)
I believe the answer is:
Here is my best explanation:
'fearsome creature' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'old woman smarter' is the subsidiary indication.
'old woman' becomes 'ma' (I've seen this in other clues).
'smarter' becomes 'neater' ('neat' can be a synonym of 'smart').
'is' is the link.
(Other definitions for maneater that I've seen before include "Vamp", "Highly-sexed, domineering woman", "Tiger, say" and "Voracious woman!".)