Noun

(en noun)

(chemistry) An isomer of a benzene derivative having two substituents adjacent on the ring

*{{quote-journal, year=1887, author=Thomas M. Morgan, title=On Some Derivatives of Ortho-Nitro-Cinnamic Acid, journal=Chemical News, date=December 21, pageurl=http://books.google.com/books?id=F-YEAAAAQAAJ&pg=RA1-PA269, url=269

, passage=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 :

*{{quote-journal, 2009, date=February 27, P. Neumann et al., Response to Comment on "Multipartite Entanglement Among Single Spins in Diamond", Science citation

, passage=Similarly, it also does not make sense to call the spin states of ortho and para hydrogen entangled. }}

(astronomy) A certain type of flat eyepiece

*{{quote-book, year=1998, title=NightWatch: A Practical Guide to Viewing the Universe, author=Terence Dickinson, page=76, pageurl=http://books.google.com/books?id=BaMBgoKPmjAC&pg=PA76

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

(photography, dated) An orthochromatic plate

*{{quote-journal, journal=Photographic Times, year=1908, page=174, pageurl=http://books.google.com/books?id=OXIAAAAAYAAJ&pg=PA174, title=On the Use of Orthochromatic Plates, author=Charles F. Rice, date=June

, passage=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.}}

(imaging) An orthophoto

*{{quote-book, year=2001, author=Drew Decker, title=GIS Data Sources, page=105, pageurl=http://books.google.com/books?id=tVmtbJ9QRxEC&pg=PA105&

, passage=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.}}

Noun

(en noun)

boundary marker

Either of the conical columns at each end of a Roman circus