spi·nous \ˈspīnəs\adjective Etymology:spine + -ous 1.: difficult or unpleasant to handle or meet : bristling, sharp, thorny < a spinous humor > 2. a.: having spines, thorns, or prickles < a spinous plant > b.: having sharp processes (as of bone) < the spinous appendage of a fish > c.: having the shape of a spine or thorn