ORTHO Meaning of ORTHO in English /awr"thoh/ , adj. Chem.pertaining to or occupying two adjacent positions in the benzene ring. Cf. meta 2 , para 3 . [ 1875-80; independent use of ORTHO- ] Random House Webster's Unabridged English dictionary. Полный английский словарь Вебстер - Random House . 2012