Of, relating to, or located at the bottom; lowest. Also: fundamental.

Of or forming the foundations or base of a building; esp. designating the cornerstone of a building (frequently in figurative contexts with…

Pertaining to, situated at, or forming the base. In Botany. Situated at the base of the ovary. basal planeand cleavage in Crystallography: one…

= basal, adj.

Forming, relating to, or of the nature of a substructure; (figurative, esp. in early use) fundamental, underlying.