SUBSTRA'TUM, noun [Latin substratus, spread under; sub and sterno.] 1. That which is laid or spread under; a layer of earth lying under another. In agriculture, the subsoil. 2. In metaphysics, the matter or substance supposed to furnish the basis in which the perceptible qualities inhere.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI