ortho-

ortho-

1.
a combining form occurring in loanwords from Greek, where it meant “straight,” “upright,” “right,” “correct” ( orthodox ) and on this model used in the formation of compound words ( orthopedic ).
2.
Chemistry.
a.
a combining form used in the name of that acid in a given series of acids that contains the most water ( orthoboric acid ). Compare meta-, pyro-.
b.
a combining form used in the names of the salts of these acids: if the acid ends in -ic, the corresponding salt ends in -ate ( orthoboric acid (H 3 BO 3 ) and potassium orthoborate (K 3 BO 3 )); if the acid ends in -ous, the corresponding salt ends in -ite ( orthoantimonous acid (H 3 SbO 3 ) and potassium orthoantimonite (K 3 SbO 3 )).
Also, especially before a vowel, orth-.

Origin:
< Greek, combining form of orthós straight, upright, correct

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Based on the Random House Dictionary, © Random House, Inc. 2013.
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Collins
World English Dictionary
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.  (often in italics) Compare meta- Compare para- o- denoting an organic compound containing a benzene ring with substituents attached to adjacent carbon atoms (the 1,2- positions): orthodinitrobenzene
5.  See meta- denoting an oxyacid regarded as the highest hydrated form of the anhydride or a salt of such an acid: orthophosphoric acid
6.  See para- denoting a diatomic substance in which the spins of the two atoms are parallel: orthohydrogen
 
[from Greek orthos straight, right, upright]
 
orth- or (before a vowel) orth-
 
—combining form
 
[from Greek orthos straight, right, upright]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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00:10
Ortho- is always a great word to know.
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an extraordinary or unusual thing, person, or event; an exceptional example or instance.
an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.
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Etymonline
Word Origin & History

ortho-
a comb. element in forming scientific and technical words, from Gk. ortho-, stem of orthos "straight, true, correct, regular," from PIE *eredh- "high" (cf. Skt. urdhvah "high, lofty, steep," L. arduus "high, steep," O.Ir. ard "high").
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

ortho- or orth-
pref.

  1. Straight; upright; vertical: orthotropic.

  2. Correct; correction: orthopsychiatry.

  3. Hydrated form of an acid or of its salts: orthoboric acid.

  4. Diatomic molecules in which the nuclei have the same direction of spin: orthohydrogen.

  5. ortho-
    Abbr. o- Of or relating to one of three possible isomers of a benzene ring with adjacent carbon atoms having attached chemical groups. Usually used in italic: ortho-dibromobenzene.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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