Consider it a brainy thing to do (5)

I believe the answer is:

think

I'm a little stuck... Click here to teach me more about this clue!

'consider' is the definition.
(I know that consider is a more specific form of the action chew over)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for think that I've seen before include "Imagine" , "Cogitate; deem" , "Believe" , "figure" , "Use one's mind" .)

I've seen this clue in the Evening Standard.

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