Coriaceous is a botanist's term for leathery in appearance, or just tough. You're not going to see it often used outside scientific contexts.
To remember this word, think of corrugated which also describes a kind of surface roughness. Or think about how courageous people like sailors and mountain climbers end up with coriaceous or leathery skin. The word itself is a lesson in historical linguistics: Coriaceous is related to the Latin word corium, which entered English in the 1650s, and traces its history back to the Pan Indo European root *(s)ker-(1), which is responsible for the Sanskrit krtih "hide," and the Old English sceran "to cut, shear."