The Collaborative International Dictionary of English v.0.48:

Sultry \Sul"try\ (s[u^]l"tr[y^]), a. [Compar. Sultrier
   (s[u^]l"tr[i^]*[~e]r); superl. Sultriest.] [From
   Sweltry.]
   1. Very hot, burning, and oppressive; as, Libya's sultry
      deserts.
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            Such as, born beneath the burning sky
            And sultry sun, betwixt the tropics lie. --Dryden.
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   2. Very hot and humid, or hot, close, stagnant, and
      oppressive, as air.
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            When in the sultry glebe I faint,
            Or on the thirsty mountain plant.     --Addison.
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