The Collaborative International Dictionary of English v.0.48:

Hawthorn \Haw"thorn`\ (h[add]"th[^o]rn`), n. [AS.
   haga[thorn]orn, h[ae]g[thorn]orn. See Haw a hedge, and
   Thorn.] (Bot.)
   A thorny shrub or tree (the Crat[ae]gus oxyacantha), having
   deeply lobed, shining leaves, small, roselike, fragrant
   flowers, and a fruit called haw. It is much used in Europe
   for hedges, and for standards in gardens. The American
   hawthorn is Crat[ae]gus cordata, which has the leaves but
   little lobed.
   [1913 Webster]

         Gives not the hawthorn bush a sweeter shade
         To shepherds?                            --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Crataegus oxyacantha
    n 1: evergreen hawthorn of southeastern Europe [syn: evergreen
         thorn, Crataegus oxyacantha]