buckthorn

Short definition from Wiktionary

Noun

1. 1
   the buckthorn family (Rhamnaceae),: especially genus Rhamnus,
2. 2
   especially genus Rhamnus,: especially common buckthorn or purging buckthorn (Rhamnus cathartica).
3. 3
   the buckthorn family (Rhamnaceae),: also alder buckthorn (Frangula), especially Frangula alnus).
4. 4
   Any of several, often thorny shrubs or small trees, especially: sea buckthorn (Hippophae, in family Elaeagnaceae).