n. (pl. strata) 1 esp. Geol. a layer or set of successive layers of any deposited substance. 2 an atmospheric layer. 3 a layer of tissue etc. 4 a a social grade, class, etc. (the various strata of society). b Statistics each of the groups into which a population is divided in stratified sampling. stratal adj.
[ L, = something spread or laid down, neut. past part. of sternere strew ]