from The American Heritage® Dictionary of the English Language, 4th Edition

  • Straight; upright; vertical: orthotropous.
  • Perpendicular: orthorhombic.
  • Correct; correction: orthopsychiatry.
  • The most fully hydrated form of an acid or of its salts: orthoboric acid.
  • Diatomic molecules in which the nuclei have the same spin direction: orthohydrogen.
  • 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • straight, right, proper
  • Having an extra proportion of water
  • in isomeric benzene derivatives, having the two substituents in adjacent positions (compare meta- and para-)
  • of any molecule of the form X2 in which the two nuclei have parallel spin

from the GNU version of the Collaborative International Dictionary of English

  • A combining form signifying straight, right, upright, correct, regular.
  • A combining form (also used adjectively)
  • The one of several acids of the same element (as the phosphoric acids), which actually occurs with the greatest number of hydroxyl groups. Cf. Normal.
  • Connection with, or affinity to, one variety of isomerism, characteristic of the benzene compounds; -- contrasted with meta- or para-; ; hence, designating any substance showing such isomerism.

from The Century Dictionary and Cyclopedia

  • n. An element in many words of Greek origin, its presence bringing in the sense of ‘straight,’ ‘upright,’ ‘right,’ ‘correct.’


Middle English, from Old French, from Latin, from Greek, from orthos, straight, correct, right.
(American Heritage® Dictionary of the English Language, Fourth Edition)
Ancient Greek ὀρθός (orthos). (Wiktionary)


Sorry, no example sentences found.


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