(1):

(n.) A sharp appendage to any of a plant; a thorn.

(2):

(n.) A rigid and sharp projection upon any part of an animal.

(3):

(n.) One of the rigid and undivided fin rays of a fish.

(4):

(n.) The backbone, or spinal column, of an animal; - so called from the projecting processes upon the vertebrae.

(5):

(n.) Anything resembling the spine or backbone; a ridge.