An Etymological Dictionary of Astronomy and Astrophysics

A generalization of the simplest closed configuration that can be made from straight line segments. For example, a → triangle is a 2-simplex because it is in two → dimensions, and → tetrahedron is a 3-simplex because it is in three dimensions (Steven Schwartzman, An Etymological Dictionary of Mathematical Terms Used in English, 1994).

Etymology (EN): Simplex, literally “uncomplicated, → simple,” from sim-, from PIE root *sem- “one, once, together” + plek- “to fold.” “folded [only] once.”

Etymology (PE): Taktâft, literally “folded once,” from tak “→ single, alone,” + tâft, contraction of tâfté “plated, twisted, fold,” as in hamtâft, → complex.