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Webster 1913 Edition

adv.

In a plaguing manner; vexatiously; extremely.

[Colloq.]

“Ronsard is so plaguily stiff and stately.”

Landor.

adv.

Vexatiously; in a manner to vex,harass or embarrass; greatly; horribly. [In vulgar use.]

plaguily ‎(comparative more plaguily, superlative most plaguily)