from The American Heritage® Dictionary of the English Language, 5th Edition.

  • adjective Consisting of four; in fours.
  • adjective Of, relating to, or being the period of geologic time from about 1.8 million years ago to the present, the more recent of the two periods of the Cenozoic Era. It is characterized by the appearance and development of humans and includes the Pleistocene and Holocene Epochs.
  • adjective Chemistry Relating to a nonhydrogen atom bonded to four other nonhydrogen atoms, especially to four carbon atoms.
  • noun The number four.
  • noun The member of a group that is fourth in order.
  • noun The Quaternary Period.

from The Century Dictionary.

  • Fourfold or tetragonal: said of the symmetry of crystals. See symmetry, 6.
  • 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.
  • noun A group of four things.

from the GNU version of the Collaborative International Dictionary of English.

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

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

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

  • adjective consisting of or especially arranged in sets of four
  • noun the cardinal number that is the sum of three and one
  • noun last 2 million years
  • adjective 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; see kwetwer- in Indo-European roots.]

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