The Collaborative International Dictionary of English v.0.48:

Smutty \Smut"ty\, a. [Compar. Smuttier; superl. Smuttiest.]
   1. Soiled with smut; smutted.
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   2. Tainted with mildew; as, smutty corn.
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   3. Obscene; not modest or pure; as, a smutty saying.
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            The smutty joke, ridiculously lewd.   --Smollett.
      [1913 Webster] -- Smut"ti*ly, adv. -- Smut"ti*ness, n.
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