Prefix · correction · straight
Means "straight" or "correct": orthodontist, orthopedic, orthodox, orthography, orthogonal.
Written by Bryan López, English teacher · Updated
Ortho- comes from Greek "orthos" (straight, correct, true) and appears in medical, scientific, and religious vocabulary. Orthodontist = dentist who straightens teeth; orthopedic = relating to correcting bones and muscles; orthodox = of correct belief; orthography = correct writing. Spanish equivalent "orto-" mirrors all of these: ortodoxo, ortopedia, ortodoncia, ortografía.
In medicine, ortho- signals correction or alignment: orthopedics (straightens bones), orthodontics (straightens teeth), orthoptics (corrects vision). In geometry: orthogonal (at right angles). In language: orthography (correct spelling), orthodox (the right doctrine). Recognising orto- in Spanish makes every ortho- word transparent in English.
Combines mainly with Greek roots in medical, scientific, and religious contexts:
Pronunciation: /ˈɔːr.θoʊ/. The th is always /θ/ as in "think", never /t/ or /d/. Spanish cognates mirror every form: ortodoncia (orthodontics), ortopedia (orthopedics), ortodoxo (orthodox), ortografía (orthography).
ortho-/ˈɔːr.θoʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Spanish speakers often default to /t/ because Spanish lacks the /θ/ phoneme. "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
Ortho- = straight, correct. Direct Spanish cognates: ortodoxo (orthodox), ortopedia (orthopedics), ortodoncia (orthodontics), ortografía (orthography). Know the orto- form in Spanish and you already know ortho- in English.
Exercise 1 · Form the word
Exercise 2 · Pick the right one
An orthodontist specialises in...
The prefix ortho- means "straight" or "correct": orthodontist, orthopedic, orthodox, orthography, orthogonal. In Spanish it usually maps to orto-.
The prefix ortho- is pronounced /ˈɔːr.θoʊ/. For example, "orthodox".
"dox" becomes "orthodox". It is a typical example of the ortho- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.