ortho-

ortho-

or orth-

pref.

1. Straight; upright; vertical: orthotropous.

2. Perpendicular: orthorhombic.

3. Correct; correction: orthopsychiatry.

4. The most fully hydrated form of an acid or of its salts: orthoboric acid.

5. Of or relating to one of three possible isomers of a benzene ring with two attached chemical groups in which the carbon atoms with attached groups are adjacent: ortho-dibromobenzene.

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[Middle English, from Old French, from Latin, from Greek, from orthos, straight, correct, right.]

ortho-

or before a vowel

orth-

combining form

1. straight or upright: orthotropous.

2. perpendicular or at right angles: orthoclastic.

3. correct or right: orthodontics; orthodox; orthography; orthoptics.

4. (Chemistry) (often in italics) denoting an organic compound containing a benzene ring with substituents attached to adjacent carbon atoms (the 1,2- positions): orthodinitrobenzene. Abbreviation: o- Compare meta-⁴ Compare para-¹⁶

5. (Chemistry) denoting an oxyacid regarded as the highest hydrated form of the anhydride or a salt of such an acid: orthophosphoric acid. See meta-⁶

6. (Chemistry) denoting a diatomic substance in which the spins of the two atoms are parallel: orthohydrogen. See para-¹⁸

[from Greek orthos straight, right, upright]

or•tho

(ˈɔr θoʊ)

adj.

pertaining to or occupying two adjacent positions in the benzene ring. Compare meta, para ².

[1875–80; independent use of ortho-]

ortho-

1. a combining form meaning “straight,” “upright,” “right,” “correct”: orthodontics; orthopedic.

2.

a. a combining form used in the name of the most hydrated acid in a given series: orthoboric acid. Compare meta- (def. 2a), pyro- (def. 2a).

b. a combining form used in the names of benzene derivatives in which the substituting group occupies the ortho position in the benzene ring.

Also, esp. before a vowel, orth-.

[< Greek, comb. form of orthós straight, upright, correct]