noun
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 ; see kwēt- in Indo-European roots.