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• tertiary
  tertiary

  adjective

  of the third order, rank, stage, formation, etc.; third.
• Tertiary
  Tertiary

  adjective

  of, denoting, or formed in the first period of the Cenozoic era, which lasted for 63 million years, during which mammals became dominant

tertiary

American  

[tur-shee-er-ee, tur-shuh-ree] / ˈtɜr ʃiˌɛr i, ˈtɜr ʃə ri /

adjective

1. 

   of the third order, rank, stage, formation, etc.; third.

2. Chemistry.

   1. noting or containing a carbon atom united to three other carbon atoms.

   2. formed by replacement of three atoms or groups.

3. (initial capital letter) noting or pertaining to the period forming the earlier part of the Cenozoic Era, occurring from 65 million to 2 million years ago, characterized by the development and proliferation of mammals.

4. Ornithology. tertial.

5. Ecclesiastical. noting or pertaining to a branch, or third order, of certain religious orders that consists of lay members living in community regular tertiaries or living in the world secular tertiaries.

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noun

• tertiaries
  plural

1. (initial capital letter) the Tertiary Period or System.

2. Ornithology. a tertial feather.

3. (often initial capital letter) a member of a tertiary branch of a religious order.

4. tertiary color.

Tertiary ¹ British  

/ ˈtɜːʃərɪ /

adjective

1. of, denoting, or formed in the first period of the Cenozoic era, which lasted for 63 million years, during which mammals became dominant

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noun

1. the Tertiary period or rock system, divided into Palaeocene, Eocene, Oligocene, Miocene, and Pliocene epochs or series

tertiary ² British  

/ ˈtɜːʃərɪ /

adjective

1. third in degree, order, etc

2. (of education) taking place after secondary school, such as at university, college, etc

3. (of an industry) involving services as opposed to extraction or manufacture, such as transport, finance, etc Compare primary secondary

4. RC Church of or relating to a Third Order

5. chem

   1. (of an organic compound) having a functional group attached to a carbon atom that is attached to three other groups

   2. (of an amine) having three organic groups attached to a nitrogen atom

   3. (of a salt) derived from a tribasic acid by replacement of all its acidic hydrogen atoms with metal atoms or electropositive groups

6. Also called: tertial.  rare ornithol of, relating to, or designating any of the small flight feathers attached to the part of the humerus nearest to the body

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noun

1. Also called: tertial.  rare ornithol any of the tertiary feathers

2. RC Church a member of a Third Order

tertiary Scientific  

/ tûr′shē-ĕr′ē /

1. Tertiary. The first period of the Cenozoic Era, from about 65 to 2 million years ago. During this time the continents took on their present form, and the climate changed from being warmer and wetter, in the early part of the period, to being drier and cooler in the later part. Mammals replaced dinosaurs as the dominant form of terrestrial animal life, and many modern types of flowering plants, insects, mollusks, fish, amphibians, reptiles, and birds appeared. The Tertiary is subdivided into the Paleogene and the Neogene, although these terms are not as widely used as are the names of the epochs that constitute them.

2. See Chart at geologic time

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1. 1. Relating to or having a carbon atom that is attached to three other carbon atoms in a molecule.

   2. Relating to an organic molecule, such as an alcohol, in which the functional group is attached to a tertiary carbon.

2. Relating to an advanced level of medical care, usually provided by subspecialists after the delivery of primary medical care.

3. Compare primary secondary

Other Word Forms

Derived Forms

• post-Tertiary
  adjective
• pre-Tertiary
  adjective

Inflected Forms

Nouns

• tertiaries
  plural

Etymology

Origin of tertiary

1540–50; < Latin tertiārius of third part or rank, equivalent to terti ( us ) third + -ārius -ary

Explanation

Tertiary is another way of saying "third in importance," like socializing with co-workers being a tertiary reason for getting an after-school job — less important than, first, earning money and second, gaining skills. To correctly pronounce tertiary, say "TER-she-err-ee." If you are the third child born in your family, don't be tempted to call yourself the "tertiary child." This means you are less important that your two older siblings. However, in some cases, tertiary does not have to do with ranking third — the Tertiary period marks the beginning of life for mammals, and in the United Kingdom, tertiary education means "college-level."

Example Sentences

See Examples For:

tertiary Tertiary tertiaries

In the Arctic Yukon, however, the cats occupied a very different ecological role as tertiary consumers and likely specialized in anadromous fish such as salmon.

From Science Daily ● Sep. 8, 2026

Investors instead have been gravitating to what Morgan Stanley analyst Joe Moore described as “secondary and tertiary AI beneficiaries” that are also benefiting from the booming investment cycle.

From The Wall Street Journal ● May 21, 2026

It has taken time for investor enthusiasm to return to the story, as the secondary and tertiary beneficiaries of AI continue to outperform, Moore noted on Monday.

From Barron's ● May 18, 2026

LeBron James exemplified the mantra when he shape-shifted from the high-usage star he’s been for more than two decades to the most accomplished tertiary option in NBA history.

From Los Angeles Times ● May 9, 2026

He might dissect, anatomise, and give names; but, not to speak of a final cause, causes in their secondary and tertiary grades were utterly unknown to him.

From "Frankenstein" by Mary Shelley

Tertiary sources frequently placed in the secondary-source category include reference materials such as encyclopedias, textbooks, manuals, digests, and bibliographies.

From Textbooks ● Dec. 21, 2021

This is called the KT boundary, because it marks the dividing line between the Cretaceous period and the Tertiary period.

From The New Yorker ● Mar. 29, 2019

Also, "Tertiary care centers tend to be much better in taking care of the out-of-the ordinary, unusual cancers," he says.

From US News ● Jul. 21, 2015

Peter Jasonides, managing director of Melbourne's Institute of Tertiary and Higher Education Australia, warns it is a tough road.

From Reuters ● Jul. 1, 2015

The Tertiary age, or age of Mammals, when the mammalia, or quadrupeds, abounded, and were the dominant race.

From Webster's Unabridged Dictionary by Noah Webster

And the colors are luscious, richly blended primaries and secondaries and tertiaries that are saturated and sensual and accentuated with blinding highlights.

From Los Angeles Times ● Feb. 23, 2019

Many tertiaries, in course of time, desired to take solemn vows and live in community, while still conforming to the rule of the Third Order; thus arose various congregations of tertiary monks and nuns.

From The Philippine Islands, 1493-1898 — Volume 21 of 55 1624 Explorations by early navigators, descriptions of the islands and their peoples, their history and records of the catholic missions, as related in contemporaneous books and manuscripts, showing the political, economic, commercial and religious conditions of those islands from their earliest relations with European nations to the close of the nineteenth century. by James Alexander Robertson

It should be borne in mind that the semi-neutrals, like the secondaries and tertiaries, may be so compounded as to be permanent, semi-stable, or fugitive.

From Field's Chromatography or Treatise on Colours and Pigments as Used by Artists by Thomas Salter

Combined with the primary blue, yellow furnishes all the variety of the secondary green, as well as, subordinately, the tertiaries russet and olive.

From Field's Chromatography or Treatise on Colours and Pigments as Used by Artists by Thomas Salter

In Diagram II we have arranged at opposite points the primaries 1, the secondaries 2, the tertiaries 3, the quaternaries 4.

From Color Value by C. R. (Chandler Robbins) Clifford