icosahedron

The term 'icosahedron' is a modern scientific compound formed directly from ancient Greek components. The first element, 'icosa-', derives from the Greek word for twenty, εἴκοσι (eíkosi), which itself has a deep Indo-European lineage. The second element, '-hedron', comes from the Greek ἕδρα (hédra), originally meaning 'seat' or 'base', which in geometric terminology was adopted to denote the flat faces of a polyhedron. Thus, the word's construction follows a perfectly literal and descriptive logic: it names the three-dimensional shape by its most defining property—a body with twenty faces.

Structure: icosa (twenty) + hedron (base, face) icosa (from Greek εἴκοσι (eíkosi), meaning 'twenty'); hedron (from Greek ἕδρα (hédra), meaning 'seat, base, face of a geometric solid').