Emily Dickinson Lexicon

STRA'TUM, n. [plur. Stratums or Strata. The latter is most common. L. from sterno, to spread or lay; Sax. streone.]

1. In geology and mineralogy, a layer; any species of earth, sand, coal and the like, arranged in a flat form, distinct from the adjacent matter. The thicker strata are called beds; and these beds are sometimes stratified.
2. A bed or layer artificially made.