The Collaborative International Dictionary of English v.0.48:

Medlar \Med"lar\, n. [OE. medler medlar tree, OF. meslier, F.
   n['e]flier, L. mespilum, mespilus, Gr. ?, ?. Cf.
   Naseberry.]
   A tree of the genus Mespilus (Mespilus Germanica); also,
   the fruit of the tree. The fruit is something like a small
   apple, but has a bony endocarp. When first gathered the flesh
   is hard and austere, and it is not eaten until it has begun
   to decay.
   [1913 Webster]

   Japan medlar (Bot.), the loquat. See Loquat.

   Neapolitan medlar (Bot.), a kind of thorn tree (Crataegus
      Azarolus); also, its fruit.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Mespilus germanica
    n 1: small deciduous Eurasian tree cultivated for its fruit that
         resemble crab apples [syn: medlar, medlar tree,
         Mespilus germanica]