ortho

noun

1. (countable)An isomer of a benzene derivative having two substituents adjacent on the ring.

   “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.”

2. (countable)A certain type of flat eyepiece.

   “Orthos are excellent eyepieces, still preferred by some backyard astronomers for medium- and high-power applications, especially planetary observing.”

3. (countable, dated)An orthochromatic plate.

   “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.”

4. (abbreviation, alt-of, clipping, countable)Clipping of orthography.
5. (abbreviation, alt-of, clipping, countable)Clipping of orthophoto.

   “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.”

6. (abbreviation, alt-of, clipping, uncountable)Clipping of orthopedics.