The Collaborative International Dictionary of English v.0.48:
Plaguily \Pla"gui*ly\, adv. In a plaguing manner; vexatiously; extremely. [Colloq.] "Ronsard is so plaguily stiff and stately." --Landor. [1913 Webster]WordNet (r) 3.0 (2006):
plaguily adv 1: in a disagreeable manner; "it's so plaguey cold!" [syn: plaguey, plaguy, plaguily]