Main Entry: stra·tum

Pronunciation: \ˈstrā-təm, ˈstra-\

Function: noun

Inflected Form(s): plural stra·ta \ˈstrā-tə, ˈstra-\

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

Date: 1599

1 : a bed or layer artificially made
2 a : a sheetlike mass of sedimentary rock or earth of one kind lying between beds of other kinds b : a region of the sea or atmosphere that is analogous to a stratum of the earth c : 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 a : a part of a historical or sociological series representing a period or a stage of development b : a socioeconomic level of society comprising persons of the same or similar status especially with regard to education or culture
4 : one of a series of layers, levels, or gradations in an ordered system <strata of thought>
5 : a statistical subpopulation

usage 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.