The Collaborative International Dictionary of English v.0.48:

Marmalade \Mar"ma*lade\ (m[aum]r"m[.a]*l[=a]d), n. [F.
   marmelade, Pg. marmelada, fr. marm['e]lo a quince, fr. L.
   melimelum honey apple, Gr. meli`mhlon a sweet apple, an apple
   grafted on a quince; me`li honey + mh^lon apple. Cf.
   Mellifluous, Melon.]
   A preserve or confection made of the pulp of fruit, as the
   quince, pear, apple, orange, etc., boiled with sugar, and
   brought to a jamlike consistency.
   [1913 Webster]

   Marmalade tree (Bot.), a sapotaceous tree (Lucuma
      mammosa) of the West Indies and Tropical America. It has
      large obovate leaves and an egg-shaped fruit from three to
      five inches long, containing a pleasant-flavored pulp and
      a single large seed. The fruit is called marmalade, or
      natural marmalade, from its consistency and flavor. [1913
      Webster]

WordNet (r) 3.0 (2006):

marmalade tree
    n 1: tropical American tree having wood like mahogany and sweet
         edible egg-shaped fruit; in some classifications placed in
         the genus Calocarpum [syn: marmalade tree, mammee,
         sapote, Pouteria zapota, Calocarpum zapota]