per·pen·dic·u·lar 
(pûr′pən-dĭkyə-lər)
(pûr′pən-dĭkyə-lər)adj.
1. Mathematics Intersecting at or forming right angles.
2. Being at right angles to the horizontal; vertical. See Synonyms at vertical.
3. often Perpendicular Of or relating to a style of English Gothic architecture of the 1300s and 1400s, characterized by the use of fan vaulting and broad windows with many mullions.
adv.
In a perpendicular position.
n.
1. Mathematics A line or plane perpendicular to a given line or plane.
2. A perpendicular position.
3. A device, such as a plumb line, that is used in marking the vertical from a given point.
4. A vertical or nearly vertical line or plane.
[Middle English perpendiculer, from Old French, from Latin perpendiculāris, from perpendiculum, plumb line, from perpendere, to weigh carefully : per-, per- + pendere, to weigh; see (s)pen- in the Appendix of Indo-European roots.]
per′pen·dic′u·lari·ty (-lărĭ-tē) n.
per′pen·dicu·lar·ly adv.