'dihedral' originates from Modern Latin/Greek roots, ultimately via French 'dièdre' (French) and New Latin, where the Greek prefix 'di-' meant 'two' and Greek 'hēdra' (ἕδρα) meant 'seat' or 'face'.

'dihedral' changed from French 'dièdre' (from Greek components) into English mathematical usage in the 18th–19th centuries and became the modern English word 'dihedral'.

Initially it referred to 'having two faces/seats'; over time it evolved to mean specifically 'relating to two planes or the angle between them' (and, by extension, the wing angle in aeronautics).