- Connection with or affinity to, one variety of isomerism, characteristic of the benzene compounds; -- contrasted with meta- or para-; as, the ortho position; hence, designating any substance showing such isomerism; as, an ortho compound.
- The one of several acids of the same element (as the phosphoric acids), which actually occurs with the greatest number of hydroxyl groups; as, orthophosphoric acid. Cf. Normal.
- A combining form signifying straight, right, upright, correct, regular; as, orthodromy, orthodiagonal, orthodox, orthographic.
- A combining form (also used adjectively).
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). ortho-. Retrieved September 22, 2026, from http://smartdefine.org/ortho-/definitions/2039555 |
| Chicago | Webster's. 2011. "ortho-" http://smartdefine.org/ortho-/definitions/2039555 (accessed September 22, 2026). |
| Harvard | Webster's 2011, ortho-, Smart Define, viewed 22 September, 2026, <http://smartdefine.org/ortho-/definitions/2039555>. |
| MLA | Webster's. "ortho-" 27 May 2011. Web. 22 September 2026. <http://smartdefine.org/ortho-/definitions/2039555> |