Plainly
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perpendicular
nounPUR-pən-DIK-yuh-ler
meaning in plain English
A straight line that meets another straight line forming a perfect L shape.
Imagine a T‑shaped nail hitting a wall; it stops perpendicular, making a perfect L.
for example
We drew a perpendicular to the road to mark where the new sidewalk would start.
If you hold a ruler straight up against a table, the ruler is a perpendicular to the tabletop. It sticks up at a perfect right‑angle, making a clear L‑shaped meeting point.