/ ˌpɜːpənˈdɪkjələ(r); NAmE ˌpɜːrp-/ adjective , noun
■ adjective
1.
perpendicular (to sth) (usually technical ) forming an angle of 90° with another line or surface; vertical and going straight up :
Are the lines perpendicular to each other?
The staircase was almost perpendicular (= very steep) .
2.
Perpendicular ( architecture ) connected with a style of architecture common in England in the 14th and 15th centuries, that makes use of vertical lines and wide arches
■ noun
the perpendicular [ sing. ] a line, position or direction that is exactly perpendicular :
The wall is a little out of the perpendicular.
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WORD ORIGIN
late Middle English (as an adverb meaning at right angles ): via Old French from Latin perpendicularis , from perpendiculum plumb line, from per- through + pendere to hang.