An Etymological Dictionary of Astronomy and Astrophysics

Prefix denoting right, straight, correct.

Prefix indicating that an organic compound contains a benzene ring substituted in the 1.2 position.

Etymology (EN): Ortho-, from Gk. orthos “set upright, straight, true, correct, regular;” cf. L. arduus “high, steep,” O.Ir. ard “high;” also cognate with Av. ərəduua-, as below; from PIE *eredh- “high.”

Etymology (PE): Ardâ-, from Av. ərəduua- “upright, erect, risen;” cf. Skt. ūrdhvá- “upright, tending upward, high;” Gk. ortho, as above.