A buckthorn (Rhamnus purshiana syn. Frangula purshiana) native to western North America, the bark of which is the source of cascara sagrada.
Origin of cascara-buckthorn
- Spanish cáscara bark from cascar to break off from Vulgar Latin quassicāre from Latin quassāre frequentative of quatere to shake kwēt- in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition