Ferret's food (4)

I believe the answer is:

grub

I believe this is a double definition.

'ferret's' is the first definition.
('grub' can be a synonym of 'ferret')

'food' is the second definition.
(grub is a kind of food)

(Other definitions for grub that I've seen before include "food, commonly" , "Insect larva or slang food (4)" , "Worm-like larva of an insect" , "Slangy food or kind of larva" , "Larva; dig shallowly" .)

I've seen this clue in The Independent.

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