1Unknowingly, unwittingly; unintentionally.
In later use probably reflecting a misapprehension of a colloquial or regional pronunciation of unknowingly.
2 rare In an unknown manner; especially in a manner or to an extent that is not known or understood; incomprehensibly; mysteriously.
Late 15th century; earliest use found in Trevisa's Bartholomeus De Proprietatibus Rerum. From unknown + -ly.