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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.
  1. 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-.
  2. 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. 2014.
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British Dictionary definitions for ortho-

ortho-

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) denoting an organic compound containing a benzene ring with substituents attached to adjacent carbon atoms (the 1,2- positions) orthodinitrobenzene, o- Compare oarsman Compare oarsman
5.
denoting an oxyacid regarded as the highest hydrated form of the anhydride or a salt of such an acid orthophosphoric acid See meta- (sense 6)
6.
denoting a diatomic substance in which the spins of the two atoms are parallel orthohydrogen See para-1 (sense 8)
Word Origin
from Greek orthos straight, right, upright
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for ortho-

before vowels orth-, word-forming element meaning "straight, upright, rectangular, regular; true, correct, proper," now mostly in scientific and technical compounds, from Greek ortho-, stem of orthos "straight, true, correct, regular," from PIE *eredh- "high" (cf. Sanskrit urdhvah "high, lofty, steep," Latin arduus "high, steep," Old Irish ard "high").

Online Etymology Dictionary, © 2010 Douglas Harper
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ortho- in Medicine

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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Word Value for ortho

8
7
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