Stratum1. (n.) A single layer of earth or rock of one kind, usually within a series of layers, which form a rock as it lies between beds of other kinds. Also used figuratively.
2. (n.) A bed or layer artificially made; a course.
Thesaurus Entries
Appleton layer, F layer, Heaviside-Kennelly layer, Van Allen belt, band, bed, bedding, belt, blood, bracket, branch, caste, category, chemosphere, clan, class, couche, course, deck, division, estate, floor, gallery, grade, group, grouping, head, heading, ionosphere, isothermal region, kin, label, layer, ledge, level, lower atmosphere, measures, order, outer atmosphere, overlayer, overstory, photosphere, pigeonhole, plane, position, predicament, race, rank, rating, rubric, seam, section, sept, set, shelf, stage, standing, station, status, step, story, strain, stratification, stratosphere, subdivision, subgroup, suborder, substratosphere, substratum, superstratum, table, thickness, tier, title, topsoil, tropopause, troposphere, underlayer, understory, understratum, upper atmosphere, vein, zone