Webster's Revised Unabridged Dictionary · 1913

Wis

Wis , adverb

[Aphetic form of iwis, ywis; or from Icelandic viss certain. See Ywis.]

Certainly; really; indeed. [Obsolete]
As wis God helpe me. — Chaucer

Wis , transitive verb

[Due to mistaking Old English iwis certain, Anglo-Saxon 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. [Obsolete or Poetic]
Howe'er you wis. — R. Browning
Nor do I know how long it is (For I have lain entranced, I wis). — Coleridge