apothem

This term is a specialized technical word used almost exclusively in geometry and trigonometry. It describes a specific line segment in a regular polygon, serving as the inradius of the polygon's incircle. Because it is a precise mathematical definition, it lacks the metaphorical or casual usage found in general vocabulary.

In a classroom or academic setting, it is often contrasted with the radius of a polygon, which connects the center to a vertex rather than to the midpoint of a side. Using this word in a non-mathematical context would be considered incorrect or highly idiosyncratic.