wane in WordNet English dictionary

1. grow smaller
   "Interest in the project waned"
   decline  go down  wane 
   
2. become smaller
   "Interest in his novels waned"
   wane 
   
3. decrease in phase
   "the moon is waning"
   wane 
   

1. a gradual decline (in size or strength or power or number)
   ebb  ebbing  wane