from The American Heritage® Dictionary of the English Language, 4th Edition

  • adj. Consisting of four; in fours.
  • adj. Of or belonging to the geologic time, system of rocks, or sedimentary deposits of the second period of the Cenozoic Era, from the end of the Tertiary Period through the present, characterized by the appearance and development of humans and including the Pleistocene and Holocene epochs. See Table at geologic time.
  • adj. Chemistry Relating to an atom bonded to four carbon atoms: a quarternary nitrogen atom.
  • n. The number four.
  • n. The member of a group that is fourth in order.
  • n. The Quaternary Period or its system of deposits.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. Of fourth rank or order.
  • adj. Of a mathematical expression containing e.g. x4.

from the GNU version of the Collaborative International Dictionary of English

  • adj. Consisting of four; by fours, or in sets of four.
  • adj. Later than, or subsequent to, the Tertiary; Post-tertiary.
  • n. The number four.
  • n. The Quaternary age, era, or formation. See the Chart of Geology.

from The Century Dictionary and Cyclopedia

  • Consisting of four; arranged or grouped in fours.
  • [capitalized] In geology, noting that part of the geological series which is more recent than the Tertiary; Post-tertiary. (See Tertiary.)
  • In old chemistry, noting those compounds which contained four elements, as fibrin, gelatin, etc.
  • In mathematics, containing, as a quantic, or homogeneous integral function, four variables.
  • n. A group of four things.
  • Fourfold or tetragonal: said of the symmetry of crystals. See symmetry, 6.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • adj. consisting of or especially arranged in sets of four
  • n. the cardinal number that is the sum of three and one
  • n. last 2 million years
  • adj. coming next after the third and just before the fifth in position or time or degree or magnitude


from The American Heritage® Dictionary of the English Language, 4th Edition

Latin quaternārius, from quaternī, by fours, from quater, four times.

from Wiktionary, Creative Commons Attribution/Share-Alike License

From the Latin quaternārius ("containing or consisting of four"), from quaternī ("four each”, “four at a time") + -ārius (whence the English suffix -ary); compare the French quaternaire.



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  • Here's a deftly written sentence featuring quaternary in its meaning "of the fourth rank":

    "To Fred Astaire, the dance was primary — his main story — and he had it filmed accordingly. In Michael Jackson's videos, the dance was tertiary, even quaternary (after the song and the story and the filming). The camera repeatedly cuts away, and, when it comes back, it often limits itself to the upper body. Jackson didn't value his dancing enough.

    "Walking on the Moon: Michael Jackson in motion" Joan Acocella

    The New Yorker July 27, 2009, 77.

    September 24, 2009