orth-

combining form

variants or ortho-

1

: straight : upright : vertical

orthograde

2

: perpendicular

orthorhombic

3

: correct : corrective

orthodontia

4

a

: hydrated or hydroxylated to the highest degree

orthophosphoric acid

b

: involving substitution at or characterized by or having the relationship of two neighboring positions in the benzene ring

ortho-xylene

Word History

Etymology

Greek, from orthos straight, right, true; akin to Sanskrit ūrdhva high, upright

Medical Definition

orth-

prefix

variants or ortho-

1

: hydrated or hydroxylated to the highest degree

orthophosphoric acid

2

: involving substitution at or characterized by or having the relationship of two neighboring positions in the benzene ring

—abbreviation o-

ortho-xylene or o-xylene

compare meta- sense 2, para- sense 2