• Consisting of four; in fours.
  • 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.
  • Relating to a nonhydrogen atom bonded to four other nonhydrogen atoms, especially to four carbon atoms.
  • The number four.
  • The member of a group that is fourth in order.
  • The Quaternary Period.
  • Fourfold or tetragonal: said of the symmetry of crystals. See <internalXref urlencoded="symmetry">symmetry</internalXref>, 6.
  • Consisting of four; arranged or grouped in fours.
  • [<em>capitalized</em>] In <em>geology</em>, noting that part of the geological series which is more recent than the Tertiary; Post-tertiary. (See <internalXref urlencoded="Tertiary">Tertiary</internalXref>.)
  • In <em>old chemistry</em>, noting those compounds which contained four elements, as fibrin, gelatin, etc.
  • In <em>mathematics</em>, containing, as a quantic, or homogeneous integral function, four variables.
  • A group of four things.
  • Consisting of four; by fours, or in sets of four.
  • Later than, or subsequent to, the Tertiary; Post-tertiary.
  • The number four.
  • The Quaternary age, era, or formation. See the <ex>Chart</ex> of <er>Geology</er>.
  • Of fourth <xref>rank</xref> or <xref>order</xref>.
  • Of a <xref>mathematical</xref> <xref>expression</xref> containing e.g. x4.
  • consisting of or especially arranged in sets of four
  • the cardinal number that is the sum of three and one
  • last 2 million years
  • coming next after the third and just before the fifth in position or time or degree or magnitude
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