Source : Webster's Revised Unabridged Dictionary (1913)

Plaguily \Pla"gui*ly\, adv.
   In a plaguing manner; vexatiously; extremely. [Colloq.]
   ``Ronsard is so plaguily stiff and stately.'' --Landor.

Source : WordNet®

plaguily
     adv : in a disagreeable manner; "it's so plaguey cold!" [syn: {plaguey},
            {plaguy}]