What is Buckthorn?

Buckthorn definition and meaning on Dictionary terms:
any of several, sometimes thorny trees or shrubs belonging to the genus Rhamnus, especially R. frangula, the bark of which is used in medicine.Compare buckthorn family.
a tree or shrub belonging to the genus Bumelia, of the sapodilla family, especially B. lycioides, a thorny tree having elliptic leaves and large clusters of white flowers, common in the southern and part of the central U.S.


reference: https://www.dictionary.com/browse/buckthorn