adv. [ OE. ywis, iwis, AS. gewis certain; akin to D. gewis, G. gewiss, and E. wit to know. See Wit to know, and Y-. ] Certainly; most likely; truly; probably. [ Obs. or Archaic ] [ 1913 Webster ]

“Ywis, ” quod he, “it is full dear, I say.” Chaucer. [ 1913 Webster ]

She answered me, “I-wisse, all their sport in the park is but a shadow to that pleasure that I find in Plato.” Ascham. [ 1913 Webster ]

A right good knight, and true of word ywis. Spenser. [ 1913 Webster ]

☞ The common form iwis was often written with the prefix apart from the rest of the word and capitalized, as, I wis, I wisse, etc. The prefix was mistaken for the pronoun, I and wis, wisse, for a form of the verb wit to know. See Wis, and cf. Wit, to know. [ 1913 Webster ]

Our ship, I wis,
Shall be of another form than this. Longfellow. [ 1913 Webster ]