(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.