Merriam-Webster Logo
  • Dictionary
  • Thesaurus
  • Medical
  • Scrabble
  • Spanish Central
  • Learner's Dictionary


noun stra·tum \ˈstrā-təm, ˈstra-\

Simple Definition of stratum

  • : one of usually many layers of a substance (such as rock)

  • : a level of society made up of people of the same rank or position

Full Definition of stratum

plural stra·ta play \ˈstrā-tə, ˈstra-\

  1. 1 :  a bed or layer artificially made

  2. 2a :  a sheetlike mass of sedimentary rock or earth of one kind lying between beds of other kindsb :  a region of the sea or atmosphere that is analogous to a stratum of the earthc :  a layer of tissue <deep stratum of the skin>d :  a layer in which archaeological material (as artifacts, skeletons, and dwelling remains) is found on excavation

  3. 3a :  a part of a historical or sociological series representing a period or a stage of developmentb :  a socioeconomic level of society comprising persons of the same or similar status especially with regard to education or culture

  4. 4 :  one of a series of layers, levels, or gradations in an ordered system <strata of thought>

  5. 5 :  a statistical subpopulation

Usage Discussion of stratum

The plural strata has occasionally been used as a singular since the 18th century and is sometimes given the plural stratas <there was a strata of Paris which mere criticism of books fails to get hold of — Ezra Pound> <a Roman burial ground suggests stratas of corruption and decay — Connie Fletcher, Booklist>. Current evidence shows senses 2, 3b, and 4 so used, with 3b the most common. Singular strata is persistent but not frequent. Strata may someday establish itself as a singular like agenda, but that use is still not established.

Examples of stratum

  1. <the lower strata of society have been hit especially hard by this economic downturn>

  2. <the level of writing in that pop novel is several strata beneath that of serious fiction>

Origin of stratum

New Latin, from Latin, spread, bed, from neuter of stratus, past participle of sternere to spread out — more at strew

First Known Use: 1599

Other Archaeology Terms

Medical Dictionary


play play
noun stra·tum \ˈstrāt-əm, ˈstrat-\

Medical Definition of stratum

plural stra·ta \ˈstrāt-ə, ˈstrat-\play play

  1. 1:  a layer of tissue <a deep stratum of the skin>

  2. 2:  a statistical subpopulation

Seen and Heard

What made you want to look up stratum? Please tell us where you read or heard it (including the quote, if possible).


February 6, 2016

an official order, decree, or edict

Get Word of the Day daily email!


Take a 3-minute break and test your skills!


Which of the following refers to thin, bending ice, or to the act of running over such ice?

duvet kittly-benders spindrift pince-nez
Name That Thing

10 quick questions: hear them, spell them, and see how your skills compare to the crowd.


Test Your Knowledge - and learn some interesting things along the way.