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• quaternary
  quaternary

  adjective

  consisting of four.
• Quaternary
  Quaternary

  adjective

  of, denoting, or formed in the most recent period of geological time, which succeeded the Tertiary period nearly two million years ago

quaternary

American  

[kwot-er-ner-ee, kwuh-tur-nuh-ree] / ˈkwɒt ərˌnɛr i, kwəˈtɜr nə ri /

adjective

1. consisting of four.

2. arranged in fours.

3. (initial capital letter) noting or pertaining to the present period of earth history, forming the latter part of the Cenozoic Era, originating about 2 million years ago and including the Recent and Pleistocene Epochs.

4. Metallurgy. (of an alloy) having four principal constituents.

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noun

quaternaries plural

1. a group of four.

2. the number four.

3. (initial capital letter) the Quaternary Period or System.

quaternary ¹ British  

/ kwəˈtɜːnərɪ /

adjective

1. consisting of fours or by fours

2. fourth in a series

3. chem containing or being an atom bound to four other atoms or groups

   a quaternary ammonium compound

4. maths having four variables

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noun

1. the number four or a set of four

Quaternary ² British  

/ kwəˈtɜːnərɪ /

adjective

1. of, denoting, or formed in the most recent period of geological time, which succeeded the Tertiary period nearly two million years ago

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noun

1. the Quaternary period or rock system, divided into Pleistocene and Holocene (Recent) epochs or series

quaternary Scientific  

/ kwŏt′ər-nĕr′ē /

1. Quaternary. The second and last period of the Cenozoic Era, from about 2 million years ago to the present. During this time the continents were situated approximately as they are today, although the geography was different due to fluctuations in sea levels caused by the advance and retreat of ice sheets. Humans first appeared during this period.

2. See Chart at geologic time

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1. Relating to or having a carbon atom that is attached to four other carbon atoms in a molecule. Quaternary pentane, for example, contains five carbon atoms of which one is in the center and the other four are each attached to it.

Etymology

Origin of quaternary

1400–50; late Middle English < Latin quaternārius consisting of four, equivalent to quatern ( ī ) four at a time + -ārius -ary

Explanation

If something is quaternary, it's either the fourth in position or exists in a group of four. If you're the fourth child in your family, you can describe yourself as the quaternary sibling. In geology, the Quaternary Period (also known as the Age of Humans) got its name from being the fourth named period of geologic time. Although scientists now classify these periods in a new way, and it's no longer the fourth, the Quaternary kept its name. In math, a base four numerical system is also called a quaternary. You'll almost always find this adjective in a technical or scientific context. It derives from the Latin quater, "four."

Example Sentences

Sunway Healthcare operates its flagship quaternary hospital in Kuala Lumpur, Malaysia’s capital.

From The Wall Street Journal • Feb. 6, 2026

Sunway Healthcare operates its flagship quaternary hospital in Kuala Lumpur, the country’s capital.

From The Wall Street Journal • Nov. 5, 2025

In the new findings, which were published in Science on April 5, 2024, Scripps Research chemists show that it's possible to convert feedstock chemicals into quaternary carbons using a single, inexpensive iron catalyst.

From Science Daily • Apr. 5, 2024

The Salyerses’ unusual marriage is known as a quaternary marriage, and their sons are known as quaternary twins.

From Washington Post • Aug. 24, 2022

In some books, too, you will find the tertiary and quaternary taken out and replaced by periods of different lengths called the Palaeogene and Neogene.

From "A Short History of Nearly Everything" by Bill Bryson