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Plural of “stratum”

The plural of stratum is strata.

Why

"Stratum" comes from the Latin verb "sternere," "to spread out" or "lay down," and the noun originally described a layer laid flat, as in a bed of rock. Like "addendum" and "datum," it's a Latin second-declension neuter noun, and that grammatical class took -a in the plural, giving English "strata" directly from the Latin pattern rather than through any English-specific rule.

Geology adopted "stratum/strata" almost unchanged when the science of rock layering developed in the 18th and 19th centuries, and that scientific usage anchored the Latin plural far more firmly than happens with most borrowed Latin words — "strata" describing rock layers is essentially universal in geology, with "stratums" almost never appearing in that technical sense. The word's later extension to social layers ("social strata") carried the same plural along with it.

Usage note

"Strata" is the expected plural in virtually every context, both the geological ("layers of sedimentary strata") and the figurative social sense ("different strata of society"); "stratums" exists but reads as distinctly nonstandard to most readers and is rarely seen in edited writing.

Statisticians use a specialized technique called "stratified sampling," which deliberately divides a population into distinct strata before sampling from each one separately, specifically to ensure that smaller subgroups aren't overlooked the way simple random sampling might overlook them — a direct, functional extension of the word's geological sense of layering.

Common real mistakes

The most common mistake is using "strata" as if it were singular ("a strata of rock" or "this strata contains fossils"), treating the Latin plural as one uncountable mass the way people sometimes do with "data" — but "stratum" remains the correct singular for one individual layer. Because "stratum" itself is a somewhat rare word outside geology and sociology, many writers simply haven't encountered the singular form often enough to reach for it instinctively. Writers should also avoid pluralizing "strata" further into a nonstandard "stratas," a double-marking mistake similar to treating an already-plural word as if it still needed an English ending.

The wider pattern

"Stratum/strata" is part of the same Latin -um/-a family as "datum/data," "addendum/addenda," and "curriculum/curricula" — nouns that entered English through scientific and academic Latin and, because their technical fields still rely on the plural constantly, have shown far less drift toward a regular English -s plural than everyday borrowed words like "cactus" or "forum." Sociology borrowed the geological metaphor deliberately in the early twentieth century, describing "social strata" as layers of society stacked much like sedimentary rock, each layer shaped by the pressures and deposits of the one above it — a metaphor precise enough that the field eventually coined "stratification" as its own formal term for the process of society sorting into such layers.

Examples

Related plurals

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