The Collaborative International Dictionary of English v.0.48:

Sun \Sun\, v. t. [imp. & p. p. Sunned; p. pr. & vb. n.
   Sunning.]
   To expose to the sun's rays; to warm or dry in the sun; as,
   to sun cloth; to sun grain.
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         Then to sun thyself in open air.         --Dryden.
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