orth- Definition

ortho-
orth-
combining form

1. Signifying straight; upright.
2. Signifying at right angles; perpendicular.
3. Signifying correct; right.
4a. chem.
Signifying the names of salts and acids that contain one molecule of water more than the corresponding meta-compound;
4b. chem.
Signifying two adjacent carbon atoms of the benzene ring. Compare meta- sense 4b.

Etymology: From Greek orthos straight or correct.