Source : Webster's Revised Unabridged Dictionary (1913)

Whitethorn \White"thorn`\, n. (Bot.)
   The hawthorn.

Source : WordNet®

whitethorn
     n : thorny Eurasian shrub of small tree having dense clusters of
         white to scarlet flowers followed by deep red berries;
         established as an escape in eastern North America [syn: {English
         hawthorn}, {may}, {Crataegus laevigata}, {Crataegus
         oxycantha}]