The Collaborative International Dictionary of English v.0.48:

Jack \Jack\ (j[a^]k), n. [Pg. jaca, Malayalam, tsjaka.] (Bot.)
   A large tree, the Artocarpus integrifolia, common in the
   East Indies, closely allied to the breadfruit, from which it
   differs in having its leaves entire. The fruit is of great
   size, weighing from thirty to forty pounds, and through its
   soft fibrous matter are scattered the seeds, which are
   roasted and eaten. The wood is of a yellow color, fine grain,
   and rather heavy, and is much used in cabinetwork. It is also
   used for dyeing a brilliant yellow. [Written also jak.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Jak \Jak\, n. (Bot.)
   see 1st Jack.
   [1913 Webster]

WordNet (r) 3.0 (2006):

jak
    n 1: immense East Indian fruit resembling breadfruit; it
         contains an edible pulp and nutritious seeds that are
         commonly roasted [syn: jackfruit, jak, jack]