Source : Webster's Revised Unabridged Dictionary (1913)

Sickerly \Sick"er*ly\, Sikerly \Sik"er*ly\, adv.
   Surely; securely. [Obs.]

         But sikerly, withouten any fable.        --Chaucer.

Siker \Sik"er\, a. & adv., Sikerly \Sik"er*ly\, adv., Sikerness
\Sik"er*ness\, n., etc.
   See 2d {Sicker}, {Sickerly}, etc. [Obs.]