What does the prefix ortho- mean?
Ortho- comes from the Greek orthos, which means "straight", "correct" or "true". It appears in medical, scientific and religious terms, always with the idea of straightening or making correct.
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Prefix · correction · straight
ortho-
Means "straight" or "correct": orthodontist, orthopedic, orthodox, orthography, orthogonal.
Scientific
Written by Bryan López, English teacher · Updated
Ortho- in medicine, geometry and language
In medicine, ortho- shows the correction or alignment of bones, teeth or vision. In geometry, it talks about right angles. In language, it appears in correct writing and in belief considered correct. If you see ortho- in a word, ask yourself what is being straightened or made correct.
How it is used
Combines mainly with Greek roots in medical, scientific, and religious contexts:
- ortho- + medical rootdontist → orthodontistpedic → orthopedicptics → orthoptics
- ortho- + academic rootgraphy → orthographydox → orthodoxgonal → orthogonal
Pronunciation: /ˈɔːr.θoʊ/. The th is always /θ/ as in "think", never /t/ or /d/.
How it is pronounced
ortho-/ˈɔːr.θoʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With ortho-
In a phrase
- doxorthodoxHis orthodox approach surprised colleagues used to modern methods.
- dontistorthodontistThe orthodontist fitted her daughter with braces for two years.
- pedicorthopedicHe visited an orthopedic surgeon after the knee injury.
- graphyorthographyGood orthography reflects a careful writer's attention to detail.
- gonalorthogonalThe two axes must be perfectly orthogonal to each other.
- pedicsorthopedicsOrthopedics covers bones, joints, muscles, and the entire skeletal system.
- pticsorthopticsThe orthoptics clinic helps children whose eyes do not align.
Common mistakes
pronouncing the th in ortho- as /t/ or /d/
the th in ortho- is always /θ/ as in "think" — never /t/ or /d/
"Orthodox" = /ˈɔːr.θə.dɒks/, not /ˈɔːr.tə.dɒks/. The same Greek-origin th appears in: orthogonal, orthopedic, orthodontic. Practice: think, three, theme — then try orthodox.
A trick to remember it
Think of an orthodontist straightening teeth: ortho- = straight, correct. orthodontics, orthopedic.
Practise what you learned
Exercise 1 · Form the word
Exercise 2 · Pick the right one
An orthodontist specialises in...
Frequently asked questions
What does the prefix ortho- mean in English?
The prefix ortho- means "straight" or "correct": orthodontist, orthopedic, orthodox, orthography, orthogonal.
How do you pronounce ortho-?
The prefix ortho- is pronounced /ˈɔːr.θoʊ/. For example, "orthodox".
Can you give an example of a word with ortho-?
"dox" becomes "orthodox". It is a typical example of the ortho- prefix.
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