wane
     n : a gradual decline (in size or strength or power or number)
         [syn: {ebb}, {ebbing}]
     v 1: grow smaller; "Interest in the project waned" [syn: {decline},
           {go down}]
     2: become smaller; "Interest in his novels waned" [ant: {wax}]
     3: decrease in phase; "the moon is waning" [ant: {wax}]
Source: WordNet® 2.0