perpendicular - definition and synonyms

adjective 

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/ˌpɜː(r)pənˈdɪkjʊlə(r)/
  1. 1
    completely upright and straight

    perpendicular cliffs

    1. a.
      maths forming a 90° angle with another surface or line
      perpendicular to:

      Line A is perpendicular to line B.