basal

Basal is an adjective meaning related to a base or bottom. It comes from Latin basalis, from basis, meaning bottom, base. In scientific and professional usage it is used to indicate something that lies at the base of structures, or that serves as a foundational reference.

In medicine and anatomy, basal often refers to the bottom or base surface of a tissue. Basal cells form the deepest layer of the epidermis, and the basal lamina is a thin layer of extracellular matrix beneath epithelium. The basal ganglia are a group of subcortical nuclei involved in movement regulation. Basal metabolic rate is the energy used by the body at rest to sustain essential physiological processes, and basal cell carcinoma is the most common form of skin cancer, arising from basal cells.

In botany, basal describes parts attached to the base of a plant, such as basal leaves or a basal rosette. In evolutionary biology, basal refers to lineages or taxa that diverged early from a common ancestor, forming a basal or early-branching group within a clade.

In geology and crystallography, basal can describe the bottom plane of a crystal or mineral, as in basal plane; in stratigraphy the basal surface marks the lowest boundary of a formation. The term is also used in other disciplines to denote foundation or starting points.