The Collaborative International Dictionary of English v.0.48:

Mammee \Mam*mee"\, Mammee tree \Mam*mee" tree`\, n. [Haitian
   mamey.] (Bot.)
   A fruit tree of tropical America, belonging to the genus
   Mammea (Mammea Americana); also, its fruit, called the
   mammee apple. The latter is large, covered with a thick,
   tough ring, and contains a bright yellow pulp of a pleasant
   taste and fragrant scent. It is often called mammee apple.

   Syn: mammee apple, mammee, mamey, Mammea americana.
        [1913 Webster]

WordNet (r) 3.0 (2006):

mammee
    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]
    2: tropical American tree having edible fruit with a leathery
       rind [syn: mammee apple, mammee, mamey, mammee tree,
       Mammea americana]
    3: globular or ovoid tropical fruit with thick russet leathery
       rind and juicy yellow or reddish flesh [syn: mamey,
       mammee, mammee apple]
    4: brown oval fruit flesh makes excellent sherbet [syn:
       sapote, mammee, marmalade plum]