Definition of "whitethorn"

Crataegus monogyna, a hawthorn species native to Europe, northwest Africa and western Asia.  examples

Bursaria spinosa, a small Australian shrub.  examples

Vachellia constricta, formerly Acacia constricta, whitethorn acacia, a shrub in the family Fabaceae.  examples

Senegalia polyacantha, of India  examples

Ceanothus leucodermis, chaparral whitethorn, a shrub in the family Rhamnaceae.  examples