Spine (?), n. [L. spina thorn, the spine; akin to spica a point: cf. OF. espine, F. épine. Cf. Spike, Spinet a musical instrument, Spinny.] 1. (Bot.) A sharp appendage to any of a plant; a thorn.
2. (Zoöl.) (a) A rigid and sharp projection upon any part of an animal. (b) One of the rigid and undivided fin rays of a fish.
3. (Anat.) The backbone, or spinal column, of an animal; — so called from the projecting processes upon the vertebræ.
4. Anything resembling the spine or backbone; a ridge.