apothem
[apuhthem]

noun Geometry.
a perpendicular from the center of a regular polygon to one of its sides.
Origin of apothem
Dictionary.com Unabridged
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for apothem
Historical Examples of apothem
The "Apothem is a perpendicular from the vertex of a pyramid on a side of the base."
The Solution of the Pyramid ProblemRobert Ballard
In any pyramid, the apothem is to half the base as the area of the four sides is to the area of the base.
The Solution of the Pyramid ProblemRobert Ballard
A peculiarity of this pyramid is, that base is to altitude as apothem is to half base.
The Solution of the Pyramid ProblemRobert Ballard
I have mentioned the above to show how very nearly these ratios agree with my exact ratio of 21 to 34 half base to apothem.
The Solution of the Pyramid ProblemRobert Ballard
apothem
noun
Word Origin for apothem
C20: from apo + Greek thema, from tithenai to place
Collins English Dictionary  Complete & Unabridged 2012 Digital Edition
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