The Collaborative International Dictionary of English v.0.48:

Cortex \Cor"tex\ (k[^o]r"t[e^]ks), n.; pl. Cortices (-t?-s?z).
   [L., bark. Cf. Cork.]
   1. Bark, as of a tree; hence, an outer covering.
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   2. (Med.) Bark; rind; specifically, cinchona bark.
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   3. (Anat.) The outer or superficial part of an organ; as, the
      cortex or gray exterior substance of the brain.
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