ortho

1. (countable, chemistry) An isomer of a benzene derivative having two substituents adjacent on the ring.Examples: "When the cinnamic acid had been nitrated the ortho was separated from the para, by suspending in alcohol and leading hydrochloric acid gas into the mixture : […]."; "Similarly, it also does not make sense to call the spin states of ortho and para hydrogen entangled."countable

2. (countable, astronomy) A certain type of flat eyepiece.Examples: "Orthos are excellent eyepieces, still preferred by some backyard astronomers for medium- and high-power applications, especially planetary observing."countable

3. (countable, photography, dated) An orthochromatic plate.Examples: "Wherever the exposure is likely to be cut short— and this includes all high speed work and most portraiture — the ortho is not so suitable as the ordinary plate."countabledated

4. (countable, linguistics) Clipping of orthography.abbreviationalt-ofclippingcountable

5. (countable, photography) Clipping of orthophoto.Examples: "The typical orthophoto building process is a long one, however, and the photography that the orthos are based may be several years old before an orthophoto is ready for distribution."abbreviationalt-ofclippingcountable

6. (uncountable, medicine) Clipping of orthopedics.abbreviationalt-ofclippinguncountable