The Collaborative International Dictionary of English v.0.48:

Tegmen \Teg"men\, n.; pl. Tegmina. [L., fr. tegere, tectum, to
   cover.]
   1. A tegument or covering.
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   2. (Bot.) The inner layer of the coating of a seed, usually
      thin and delicate; the endopleura.
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   3. (Zool.) One of the elytra of an insect, especially of
      certain Orthoptera.
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   4. pl. (Zool.) Same as Tectrices.
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