The best replacement for perpendicular lines is intersecting lines.

The best alternatives to perpendicular lines are rated as following:
★★★★★  intersecting lines
★★  parallel
  intersecting
  parallel lines

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Speaking about perpendicular lines, one probably shouldn't forget about slopes.

Other search terms related to perpendicular lines and their ratings are:
★★★★★ slopes
★★★ slope intercept
You have in mind a companion for perpendicular lines and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of perpendicular lines in all years. Click on graph for more.
perpendicular lines
intersecting lines
parallel