buckthornPronunciation: /ˈbʌkθɔːn/Definition of buckthorn noun a shrub or small tree which typically bears thorns and black berries. Some kinds yield dyes and others have been used medicinally. Genus Rhamnus, family Rhamnaceae: several species, including the common buckthorn (R. cathartica), with berries formerly used as a cathartic. Origin: late 16th century: from buck1 in the sense 'deer' + thorn, translating modern Latin spina cervinabuckthorn in other Oxford dictionaries Definition of buckthorn in the US English dictionary