The Collaborative International Dictionary of English v.0.48:
Spinous \Spi"nous\, a. 1. Spinose; thorny. [1913 Webster] 2. Having the form of a spine or thorn; spinelike. [1913 Webster] Spinous process of a vertebra (Anat.), the dorsal process of the neural arch of a vertebra; a neurapophysis. [1913 Webster]