Cortex

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late Middle English: from Latin, literally ‘bark’.

wiktionary

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From Latin cortex(“cork, bark”).

etymonline

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cortex (n.)

1650s, "outer shell, husk;" in botany, zoology, anatomy, "some part or structure resembling bark or rind," from Latin cortex "bark of a tree" (from PIE root *sker- (1) "to cut"). Specifically of the brain, by 1741.