Definition of perpendicular:

part of speech: adjective

Hanging or extending in a right line from any point; at right angles to any plane or line; vertical.

Usage examples:

• You feel that you must walk in measured step and place your hat precisely perpendicular for the eyes of 'Society' are upon you. Richard Jefferies in "Hodge and His Masters".

• The ravine, which was quite wide at its opening, changed into a dell, locked in on two sides by perpendicular rocks, and on its bottom a few trees grew. Henryk Sienkiewicz in "In Desert and Wilderness".