stratum

Etymology

It is borrowed from New Latin strātum,^[2][3][4][5] a specific use of classical Latin strātum (“something spread or laid down; bedding, coverlet, saddlecloth, pavement”),^[5][3][2] the neuter past participle of sternō (“to spread out, lay down, strew”).^[5][3][6][7] The OED records the geological use in post-classical Latin from 1669.^[5] It thinks the Latin verb apparently merges an older verb meaning to spread or scatter, with the same base as Ancient Greek στόρνυναι (stórnunai, “to spread out”) and Old Irish sernaid (“he spreads out”), with a homonym meaning to level or knock down, with the same base as στρατός (stratós, “army”).^[5] Etymonline derives it from a nasalized form of Proto-Indo-European *stere- (“to spread”),^[3] and Klein relates it to strāmen (“straw”), struō (“to put together, construct”) and, within Germanic, to Old English strēowian (“to strew, scatter”), the source of strew.^[8] Merriam-Webster's Unabridged adds Middle Irish srath (“wide valley”).^[7]

Earliest recorded meaning

A quantity of a substance spread over a surface, a thin layer or coating: 1599, in A. M.'s translation of Gaebelkhover's Boock of Physicke.^[5][7] Barnhart, Etymonline and Dictionary.com give the same date or decade.^[2][3][9]

Semantic evolution

The word was first a general term for a layer of any material, and the OED ties its use for repeated layers to the phrase stratum upon stratum, after a post-classical Latin phrase.^[5] The geological sense, a natural bed of rock laid down in one period, is recorded from 1671, in a translation of Steno, and the OED takes it from the Latin geological use.^[5] Johnson (1755) gave just "a bed; a layer" and called it a term of philosophy, quoting Woodward on a stratum of stone in a Cumberland iron mine.^[10] Specialists then applied it to their own layers: animal and plant tissue (1698), regions of the air or sea (1751), archaeological levels (1853), vegetation in a forest (1901) and, in stratified sampling, subgroups of a population (1920).^[5] Chiefly from the geological sense came figurative uses, first (1807) for a level or period within a series,^[5][4] and then, from 1819, in W. Irving, for a social class.^[5]

Timeline

• 1599 – a layer or coating of a substance.^[5][2]
• 1671 – a natural layer or bed of rock.^[5]
• 1698 – a layer of animal or plant tissue.^[5]
• 1751 – a region of the atmosphere or sea, bounded by horizontal planes.^[5]
• 1807 – figuratively, one of a series of levels or periods.^[5]
• 1819 – a level of society.^[5]
• 1853 – a level in an archaeological site.^[5]
• 1856 – a striation in an electrical discharge.^[5]
• 1901 – a layer of vegetation in a plant community.^[5]
• 1920 – a subgroup of a population in stratified sampling.^[5]

Meanings

Noun

1. A layer of sedimentary rock or earth, usually one of a series: The cliff shows a stratum of chalk above the clay.^[11][7][5]
2. A layer of any material, especially one of several parallel layers.^[11][9][5]
3. A level of a social hierarchy, marked by such things as status, education or income: families from every stratum of the town.^[11][5]
4. A single layer of tissue or cells.^[11][5]
5. A layer of the atmosphere or the ocean, natural or marked off for study.^[11][5]
6. A level in an archaeological site, with the remains found in it.^[5][4]
7. (ecology) A layer of vegetation in a plant community, especially a forest.^[5][4]
8. (statistics) One of the subgroups into which a population is divided for sampling.^[5]

Word family

• stratal
• stratous
• adstratum
• stratigraphic
• stratigraphy
• substratum
• superstratum
• understratum

Related words

• stratification
• stratify
• stratosphere
• stratus
• strew
• street
• stratagem
• strategy
• prostrate
• consternation
• structure
• estrade

Usage notes

The plural is usually strata, also stratums.^[7][11] The OED's first edition (1917) called stratums "not in scientific use", but the form has lasted in occasional use since the late 17th century.^[5] Dictionary.com reports strata used now and then as a singular, and more rarely a new plural stratas; usage guides condemn both.^[9] The Shorter Oxford also calls these uses non-standard.^[4]

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
3. ^ a b c d e Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
5. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z 27 28 29 30 Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
6. ^ The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
7. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
8. ^ Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
9. ^ a b c Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
10. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
11. ^ a b c d e f Collins English Dictionary (2023), Glasgow: HarperCollins