Crossword Genius

Learned grain contained only half the bran (8)

Ross

I believe the answer is:

cerebral

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'learned' is the definition.
(I know that learned can be written as cerebral)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for cerebral that I've seen before include "Highly intellectual" , "Intellectual, brainy" , "Concerning the brain" , "Relating to the brain" , "Of the brain, intellectual" .)

I've seen this clue in the Sydney Morning Herald.
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