BA'SIS, n. plu.bases. [L.and Gr.; the same as base, which see.]1. The foundation of any thing; that on which a thing stands or lies; the bottom or foot of the thing itself, or that on which it rests. See a full explanation under base.2. The ground work or first principle; that which supports.3. Foundation; support. The basis of public credit is good faith. The basis of all excellence is truth.4. Basis, in chimistry. See Base. No. 12.