Source : Webster's Revised Unabridged Dictionary (1913)

Wis \Wis\, adv. [Aphetic form of iwis, ywis; or fr. Icel. viss
   certain. See {Ywis}.]
   Certainly; really; indeed. [Obs.] ``As wis God helpe me.''
   --Chaucer.

Wis \Wis\, v. t. [Due to mistaking OE. iwis certain, AS. gewiss,
   for I wis. See {Ywis}.]
   To think; to suppose; to imagine; -- used chiefly in the
   first person sing. present tense, I wis. See the Note under
   {Ywis}. [Obs. or Poetic] ``Howe'er you wis.'' --R. Browning.

         Nor do I know how long it is (For I have lain
         entranced, I wis).                       --Coleridge.