The Collaborative International Dictionary of English v.0.48:

Pomelo \Pom"e*lo\, n. [Cf. Pompelmous.]
   A variety of shaddock, called also grape fruit.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pomelo
    n 1: southeastern Asian tree producing large fruits resembling
         grapefruits [syn: pomelo, pomelo tree, pummelo,
         shaddock, Citrus maxima, Citrus grandis, Citrus
         decumana]
    2: large pear-shaped fruit similar to grapefruit but with coarse
       dry pulp [syn: pomelo, shaddock]