The Collaborative International Dictionary of English v.0.48:

Pompelmous \Pom"pel*mous\, n.; pl. Pompelmouses. [D.
   pompelmoes; cf. G. pompelmuse, F. pamplemousse, and F.
   pompol['e]on.] (Bot.)
   A shaddock, esp. one of large size.
   [1913 Webster]