qua·ter·nar·y (kwŏtər-nĕr′ē, kwə-tûrnə-rē)
1. Consisting of four; in fours.
2. Quaternary Of, relating to, or being the period of geologic time from about 2.6 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. See Table at geologic time.
3. Chemistry Relating to a nonhydrogen atom bonded to four other nonhydrogen atoms, especially to four carbon atoms: a quaternary nitrogen atom.
n. pl. qua·ter·nar·ies
1. The number four.
2. The member of a group that is fourth in order.
3. Quaternary The Quaternary Period.
[Latin quaternārius, from quaternī, by fours, from quater, four times; see kwetwer- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.