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Webster 1913 Edition

adv.

In a perpendicular manner; vertically.

adv.

In a manner to fall on another line at right angles.

So as to fall on the plane of the horizon at right angles; in a direction towards the center of the earth or of gravity.

perpendicularly ‎(comparative more perpendicularly, superlative most perpendicularly)

in a perpendicular manner