WordReference Random House Unabridged Dictionary of American English © 2026
orth-,
Orth.,
orth.,
WordReference Random House Unabridged Dictionary of American English © 2026- var. of ortho- before a vowel:orthicon.
Orth.,
- Orthodox.
orth.,
- Medicineorthopedic
- Medicineorthopedics.
or•tho
(ôr′thō),USA pronunciation adj. [Chem.]
ortho-,
- Chemistrypertaining to or occupying two adjacent positions in the benzene ring. Cf. meta 2, para 3.
- independent use of ortho- 1875–80
ortho-,
- a combining form occurring in loanwords from Greek, where it meant "straight,'' "upright,'' "right,'' "correct'' (orthodox) and on this model used in the formation of compound words (orthopedic).
- Chemistry
- a combining form used in the name of that acid in a given series of acids that contains the most water (orthoboric acid). Cf. meta-, pyro-.
- Chemistrya combining form used in the names of the salts of these acids: if the acid ends in -ic, the corresponding salt ends in -ate (orthoboric acid (H3BO3) and potassium orthoborate (K3BO3));
if the acid ends in -ous, the corresponding salt ends in -ite (orthoantimonous acid (H3SbO3) and potassium orthoantimonite (K3SbO3)).
- Greek, combining form of orthós straight, upright, correct
'orth-' also found in these entries (note: many are not synonyms or translations):
halfpennyworth
- ha'p'orth
- ortho-
- word
- amphithyra
- analogion
- anorthite
- antidoron
- antimension
- apodeipnon
- apostolic succession
- Apostolos
- artophorion
- chartophylax
- contakion
- epitrachelion
- eulogia
- hesperinos
- holy bread
- kamelaukion
- kontakion
- Kyrie eleison
- laura
- mandyas
- NATO
- orthicon
- ortho
- orthodontia
- orthodontics
- orthoptic
- orthros
- patriarch
- pentecostarion
- phelonion
- phenolion
- proskomide
- prothonotary
- rason
- rasophore
- skete
- starets
- stauropegion
- sticharion
- synaxarion