GNU Collaborative International Dictionary of English

Found one definition

1.       
   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.”
   
   [1913 Webster]
   
   Then to sun thyself in open air. Dryden.
   
   [1913 Webster]