What is "ywis"

Ywis \Y*wis"\, 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]

``Ywis,'' quod he, ``it is full dear, I say.''
--Chaucer.

She answered me, ``I-wisse, all their sport in the park is but a shadow to that pleasure that I find in Plato.''
--Ascham.

A right good knight, and true of word ywis.
--Spenser.

Note: 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.

Our ship, I wis, Shall be of another form than this.
--Longfellow.

adv. (obsolete spelling of iwis English)