01 a. Exactly upright or vertical; pointing to the zenith; at right angles to the plane of the horizon; extending in a right line from any point …
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1.
Exactly upright or vertical; pointing to the zenith; at right angles to the plane of the horizon; extending in a right line from any point toward the center of the earth.
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2.
At right angles to a given line or surface; as, the line ad is perpendicular to the line bc.(Geom.)
Phrases & compounds
Perpendicular style —
a name given to the latest variety of English Gothic architecture, which prevailed from the close of the 14th century to the early part of the 16th; -- probably so called from the vertical style of its window mullions.