quaternary

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Consisting of four; in fours.
2. 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.
3. adj. Chemistry Relating to an atom bonded to four carbon atoms: a quarternary nitrogen atom.
4. n. The number four.
5. n. The member of a group that is fourth in order.
6. n. The Quaternary Period or its system of deposits.

Century Dictionary and Cyclopedia

1. Consisting of four; arranged or grouped in fours.
2. [capitalized] In geology, noting that part of the geological series which is more recent than the Tertiary; Post-tertiary. (See Tertiary.) The oldest and most general division of the Quaternary is into diluvial and alluvial, by which terms are meant respectively coarse detrital material and fine detrital material—the one the result of rapid, the other of slower currents of water. The former presence of ice, both fixed and floating, over a part of the northern hemisphere, and especially in the regions where geology was earliest cultivated, has greatly complicated the question of this division of the Quaternary into subgroups or epochs. Thus diluvial has come to be replaced for the most part by glacial; and some English geologists divide the Quaternary into glacial and recent, using the term Pleistocene also as the equivalent of glacial. The term recent has also as its synonym both alluvial and human. While the essential difference between Tertiary and Quaternary is theoretically supposed to be that in the former a portion of the fossil species are extinct, while in the latter all are living, this does not apply in the case of land-animals, especially the mammals. In fact, there is, over extensive areas, great difficulty in deciding the question whether certain formations shall be called Tertiary or Quaternary, as, for instance, in the case of the Pampean deposits, which, although containing great numbers of species of mammals all or nearly all extinct, are generally considered by geologists as being of Quaternary age.
3. In old chemistry, noting those compounds which contained four elements, as fibrin, gelatin, etc.
4. In mathematics, containing, as a quantic, or homogeneous integral function, four variables. A surface may be called a quaternary locus, because defined by a quaternary equation, or one equating a quaternary quantic to zero.
5. n. A group of four things.
6. Fourfold or tetragonal: said of the symmetry of crystals. See symmetry, 6.

Wiktionary

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

GNU Webster's 1913

1. adj. Consisting of four; by fours, or in sets of four.
2. adj. (Geol.) Later than, or subsequent to, the Tertiary; Post-tertiary.
3. n. The number four.
4. n. (Geol.) The Quaternary age, era, or formation. See the Chart of Geology.

WordNet 3.0

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