Sicker; Siker

Part of speech: adjective (a.)

Sure; certain; trusty. [Obs. or Prov. Eng. & Scot.] Burns. When he is siker of his good name. Chaucer.

Part of speech: adverb (adv.)

Surely; certainly. [Obs.] Believe this as siker as your creed. Chaucer. Sicker, Willye, thou warnest well. Spenser.