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.

Definitions of stratum

n one of several parallel layers of material arranged one on top of another (such as a layer of tissue or cells in an organism or a layer of sedimentary rock)

A horizon
the top layer of a soil profile; usually contains humus
B horizon
immediately below the A-horizon; contains deposits of organic matter leached from surface soils
C horizon
beneath the B-horizon and above the bedrock; consisting of weathered rock
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cuticle, epidermis
the outer layer of the skin covering the exterior body surface of vertebrates
corneum, horny layer, stratum corneum
the outermost layer of the epidermis consisting of dead cells that slough off
stratum lucidum
the layer of epidermis immediately under the stratum corneum in the skin of the palms and soles
stratum granulosum
the layer of epidermis just under the stratum corneum or (on the palms and soles) just under the stratum lucidum; contains cells (with visible granules) that die and move to the surface
malpighian layer, rete Malpighii, stratum basale, stratum germinativum
the innermost layer of the epidermis
corium, derma, dermis
the deep vascular inner layer of the skin
the inner layer of the periosteum
paries, wall
(anatomy) a layer (a lining or membrane) that encloses a structure
substrate, substratum
any stratum or layer lying underneath another
superstrate, superstratum
any stratum or layer superimposed on another
a specific layer or stratum of soil or subsoil in a vertical cross section of land
bed, seam
a stratum of ore or coal thick enough to be mined with profit
(geology) a stratum of rock (especially sedimentary rock)
mantle, pallium
(zoology) a protective layer of epidermis in mollusks or brachiopods that secretes a substance forming the shell
abdominal wall
a wall of the abdomen
soil horizon
a layer in a soil profile
geological horizon
a layer of rock with a particular composition (especially of fossils); for dating the stratum
coal seam
a seam of coal
ore bed
a stratum of ore
Type of:
a relatively thin sheetlike expanse or region lying over or under another

n people having the same social, economic, or educational status

class, social class, socio-economic class
Ferdinand and Isabella
joint monarchs of Spain; Ferdinand V and Isabella I
William and Mary
joint monarchs of England; William III and Mary II
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domain, world
people in general; especially a distinctive group of people with some shared interest
age class
people in the same age range
the class of people engaged in growing food
brotherhood, fraternity, sodality
people engaged in a particular occupation
estate, estate of the realm, the three estates
a major social class or order of persons regarded collectively as part of the body politic of the country (especially in the United Kingdom) and formerly possessing distinct political rights
labor, labour, proletariat, working class
a social class comprising those who do manual labor or work for wages
lower class, underclass
the social class lowest in the social hierarchy
bourgeoisie, middle class
the social class between the lower and upper classes
class consisting of all those who are considered boobs
commonality, commonalty, commons
a class composed of persons lacking clerical or noble rank
the class of peasants
a class of woman not considered respectable because of indiscreet or promiscuous behavior
the criminal class
class of small freeholders who cultivated their own land
a social class separated from others by distinctions of hereditary rank or profession or wealth
(Hinduism) a hereditary social class among Hindus; stratified according to ritual purity
upper class, upper crust
the class occupying the highest position in the social hierarchy
a class of 14th century Japanese who were trained in martial arts and were hired for espionage and assassinations
firing line
the most advanced and responsible group in an activity
immigrant class
recent immigrants who are lumped together as a class by their low socioeconomic status in spite of different cultural backgrounds
politically moderate persons; centrists
old school
a class of people favoring traditional ideas
the customers for a particular product or service
craft, trade
people who perform a particular kind of skilled work
fair sex, woman, womanhood
women as a class
Lords Spiritual, first estate
the clergy in France and the heads of the church in Britain
Lords Temporal, second estate
the nobility in France and the peerage in Britain
Commons, third estate
the common people
fourth estate
the press, including journalists, newspaper writers, photographers
labor force, labor pool
the source of trained people from which workers can be hired
(Marxism) the unorganized lower levels of the proletariat who are not interested in revolutionary advancement
organized labor
employees who are represented by a labor union
petit bourgeois, petite bourgeoisie, petty bourgeoisie
lower middle class (shopkeepers and clerical staff etc.)
academe, academia
the academic world
Grub Street
the world of literary hacks
(Hinduism) a Hindu caste or distinctive social group of which there are thousands throughout India; a special characteristic is often the exclusive occupation of its male members (such as barber or potter)
elite, elite group
a group or class of persons enjoying superior intellectual or social or economic status
aristocracy, gentry
the most powerful members of a society
people in power, ruling class
the class of people exerting power or authority
black market
people who engage in illicit trade
Type of:
(plural) any group of human beings (men or women or children) collectively

n an abstract place usually conceived as having depth

“the mind functions on many strata simultaneously”
layer, level
Type of:
an abstract mental location

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