The Collaborative International Dictionary of English v.0.48:

Incogitance \In*cog"i*tance\, Incogitancy \In*cog"i*tan*cy\, n.
   [L. incogitantia.]
   Lack of thought, or of the power of thinking;
   thoughtlessness; unreasonableness.
   [1913 Webster]

         'T is folly and incogitancy to argue anything, one way
         or the other, from the designs of a sort of beings with
         whom we so little communicate.           --Glanvill.
   [1913 Webster]