Take in a small comparison at heart (10)

I believe the answer is:

assimilate

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'take in' is the definition.
(I know that take in can be written as assimilate)

I don't understand how the rest of the clue works.

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(Other definitions for assimilate that I've seen before include "thoroughly understood" , "pick up" , "Become part of the prevailing culture" , "Absorb and digest (food)" , "Take in and understand" .)

I've seen this clue in The Daily Express.

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