Go to 'thermo-' entry Go to 'dino-' entry Go to 'chondro-' entry Go to 'aero-' entry Go to '-logy' entry Go to 'thaumato-' entry Go to 'nano-' entry Go to '-sophy' entry Go to 'bucco-' entry Go to '-ism' entry Go to '-lysis' entry Go to 'galacto-' entry Go to '-anthropy' entry Go to 'pneumo-' entry Go to '-ploitation' entry Go to '-lithic' entry Go to '-sepalous' entry Go to 'onco-' entry Go to '-parous' entry Go to 'dermato-' entry Go to 'multi-' entry Go to 'dodeca-' entry Go to '-zoon' entry Go to 'vermi-' entry Go to 'crystallo-' entry Go to 'biblio-' entry Go to 'eco-' entry Go to 'juxta-' entry Go to 'facio-' entry
Affixes: the building blocks of English
Affixes: the building blocks of English

ortho- Also o-.

Straight; correct; upright.

[Greek orthos, straight, right.]

Orthodox literally means having the correct opinion (Greek doxa, opinion); orthoepy (Greek epos, epe-, word) is the correct or accepted pronunciation of words, or the study of it; orthodontics (Greek odous, odont-, tooth) is the treatment of irregularities in the teeth and jaws; something orthogonal (Greek gōnia, angle) involves right angles.

In chemistry, the form indicates substitution at two adjacent carbon atoms in a benzene ring (orthodichlorobenzene, ortho-aminoanisole), as opposed to the other two possible positions, meta- and para-1. It is often abbreviated to o-: o-tolidine, o-hydroxybenzaldehyde.

The form can also denote a compound in the highest state of hydration, containing the maximum number of hydroxyl groups: an example is an ortho acid such as orthosilicic acid. Such acids are often unstable and lose water to form compounds designated by meta-, as orthophosphoric acid becomes metaphosphoric acid on heating.

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