The Collaborative International Dictionary of English v.0.48:

Witless \Wit"less\, a.
   Destitute of wit or understanding; wanting thought; hence,
   indiscreet; not under the guidance of judgment. "Witless
   bravery." --Shak.
   [1913 Webster]

         A witty mother! witless else her son.    --Shak.
   [1913 Webster]

         Witless pity breedeth fruitless love.    --Fairfax.
   [1913 Webster] -- Wit"less*ly, adv. -- Wit"less*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

witless
    adj 1: (of especially persons) lacking sense or understanding or
           judgment [syn: nitwitted, senseless, soft-witted,
           witless]