Definition of whitethorn:
(n) :
Crataegus monogyna, a hawthorn species native to Europe, northwest Africa and western Asia.
(n) :
Vachellia constricta, formerly Acacia constricta, whitethorn acacia, a shrub in the family Fabaceae.
(n) :
Bursaria spinosa, a small Australian shrub.
(n) :
Senegalia polyacantha, of India
(n) :
Ceanothus leucodermis, chaparral whitethorn, a shrub in the family Rhamnaceae.
(n) :
An unincorporated community in Humboldt County, California, USA; formerly, Thorn.