The Collaborative International Dictionary of English v.0.48:

Custard \Cus"tard\ (k[u^]s"t[~e]rd), n. [Prob. the same word as
   OE. crustade, crustate, a pie made with a crust, fr. L.
   crustatus covered with a crust, p. p. of crustare, fr. crusta
   crust; cf. OF. croustade pasty, It. crostata, or F. coutarde.
   See Crust, and cf. Crustated.]
   A mixture of milk and eggs, sweetened, and baked or boiled.
   [1913 Webster]

   Custard apple (Bot.), a low tree or shrub of tropical
      America, including several species of Anona (Anona
      squamosa, Anona reticulata, etc.), having a roundish or
      ovate fruit the size of a small orange, containing a soft,
      yellowish, edible pulp.

   Custard coffin, pastry, or crust, which covers or coffins a
      custard [Obs.] --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

custard apple
    n 1: any of several tropical American trees bearing fruit with
         soft edible pulp [syn: custard apple, custard apple
         tree]
    2: the fruit of any of several tropical American trees of the
       genus Annona having soft edible pulp