stratum

American  

[strey-tuhm, strat-uhm] / ˈstreɪ təm, ˈstræt əm /

noun

plural

strata, stratums

1. a layer of material, naturally or artificially formed, often one of a number of parallel layers one upon another.

   a stratum of ancient foundations.

2. one of a number of portions or divisions likened to layers or levels.

   an allegory with many strata of meaning.

3. Geology. a single bed of sedimentary rock, generally consisting of one kind of matter representing continuous deposition.

4. Biology. a layer of tissue; lamella.

5. Ecology. (in a plant community) a layer of vegetation, usually of the same or similar height.

6. a layer of the ocean or the atmosphere distinguished by natural or arbitrary limits.

7. Sociology. a level or grade of a people or population with reference to social position, education, etc..

   the lowest stratum of society.

8. Linguistics. (in stratificational grammar) a major subdivision of linguistic structure.

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stratum British  

/ ˈstrɑːtəm /

noun

1. (usually plural) any of the distinct layers into which sedimentary rocks are divided

2. biology a single layer of tissue or cells

3. a layer of any material, esp one of several parallel layers

4. a layer of ocean or atmosphere either naturally or arbitrarily demarcated

5. a level of a social hierarchy that is distinguished according to such criteria as educational achievement or caste status

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stratum Scientific  

/ strā′təm,străt′əm /

plural

strata

1. A layer of sedimentary rock whose composition is more or less the same throughout and that is visibly different from the rock layers above and below it.

2. A layer of tissue, as of the skin or another organ.

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Usage

Strata, historically the plural of stratum, is occasionally used as a singular: The lowest economic strata consists of the permanently unemployable. Less frequently, a plural stratas occurs: Several stratas of settlement can be seen in the excavation. At present, these uses are not well established, and they are condemned in usage guides. Strata may eventually become part of a group of borrowed plurals that are now used as singulars in English, such as agenda and candelabra, but it is not yet in that category. See also agenda, criterion, media, phenomena.

Other Word Forms

• stratal adjective
• stratous adjective

Etymology

Origin of stratum

1590–1600; < Latin strātum literally, a cover, noun use of neuter of strātus, past participle of sternere to spread, strew, equivalent to strā- variant stem + -tus past participle suffix

Explanation

A stratum is a layer of something, whether abstract, like a social stratum composed of only billionaires, or physical, like the different strata (that’s the plural version) of clouds that an airplane passes through. Stratum comes from the Latin meaning "something that has been laid down," like asphalt or a bedsheet, but we generally use it to describe layers of something. If you go into geology, you will probably investigate different strata of the soil. If you start out in life poor and try to become rich, you are trying to get into a different social stratum.

Example Sentences

Each stratum, or layer, of our planet tells a story.

From Los Angeles Times • Jul. 1, 2025

Simply put, only a certain stratum of Americans prioritize learning about politics.

From Salon • Dec. 13, 2024

The hard microneedles penetrate through the stratum corneum, which has high electrical resistance.

From Science Daily • Jan. 30, 2024

"Activists are worried about various charges being brought against such individuals who actively use their right to free speech. Democracy cannot exist without this stratum of people who exercise freedom of speech and thought."

From BBC • Oct. 2, 2023

In Durham’s long history, few blacks of this social stratum had attended these meetings.

From "The Best of Enemies" by Osha Gray Davidson