Stratum
Stratum , noun
[Latin, from sternere, stratum, to spread; akin to Greek {not transcribed} to spread, strew. See Strew, and compare Consternation, Estrade, Prostrate, Stratus, Street.]
1.
(Geology) A bed of earth or rock of one kind, formed by natural causes, and consisting usually of a series of layers, which form a rock as it lies between beds of other kinds. Also used figuratively.
2.
A bed or layer artificially made; a course.