Ortho-

Part of speech: noun (n.)

1. A combining form signifying straight, right, upright, correct, regular; as, orthodromy, orthodiagonal, orthodox, orthographic.

2. A combining form (also used adjectively), designating:

3. 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.