Thinks of ancient sorcerers hiding in trees, powerless (8)

I believe the answer is:

imagines

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'thinks' is the definition.
('imagine' can be a synonym of 'think')

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for imagines that I've seen before include "Dreams of" , "Conceives in the mind" , "Supposes" , "Conjures up in the mind" , "Fancies" .)

I've seen this clue in The Independent.

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