Origin: Latin suffix -al
Horizontal has 4 different meanings across 2 categories:
something that is oriented horizontally
"The picture on the wall was hung horizontal, so it looked longer than it actually was."
a horizontal component of a structure
"The engineer calculated that adding a horizontal component to the bridge's truss would significantly increase its stability against lateral wind forces."
In plain English: A horizontal line runs straight across from side to side, just like the horizon on the ground.
"The horizontal on the graph showed the steady sales figures for the year."
Usage: Use "horizontal" as a noun only in technical contexts to describe a specific part of a structure that runs side-to-side, such as the horizontal component of a beam. In everyday conversation, it is almost always an adjective describing something level or flat rather than a standalone object.
perpendicular to the vertical; parallel to the plane of the horizon; level, flat
"The shelf was installed perfectly horizontal so that no dish would slide off onto the floor."
In plain English: Horizontal means something that goes from side to side, like the horizon line you see when looking out at the sky.
"The book fell off the horizontal shelf and landed on the floor."
Usage: Use horizontal to describe a line or surface that runs side to side at the same level, such as a shelf placed parallel to the ground. Avoid using it vertically or for anything tilted upward or downward.
The word "horizontal" comes from the Middle French term horizontal, which was borrowed from the Latin word horizōn. Originally referring to the visible line where the earth meets the sky, it entered English with this same meaning.