Source : Webster's Revised Unabridged Dictionary (1913)

Water lemon \Wa"ter lem"on\ (Bot.)
   The edible fruit of two species of passion flower
   ({Passiflora laurifolia}, and {P. maliformis}); -- so called
   in the West Indies.

Source : WordNet®

water lemon
     n : the edible yellow fruit of the Jamaica honeysuckle [syn: {bell
         apple}, {sweet cup}, {yellow granadilla}]