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Definition of ortho- in English:

ortho-

Pronunciation /ˈôrTHō/ /ˈɔrθoʊ/

  • 1Straight; rectangular; upright.

    • ‘orthodontics’
    1. 1.1Right; correct.
      • ‘orthoepy’

  • 2Chemistry
    Denoting substitution at two adjacent carbon atoms in a benzene ring, e.g., in 1, 2 positions.

    Compare with meta- and para-

    • ‘orthodichlorobenzene’

  • 3Chemistry
    Denoting a compound from which a meta-compound is formed by dehydration.

    • ‘orthophosphoric acid’

Origin

From Greek orthos ‘straight, right’.