wane

Noun

• a gradual decline (in size or strength or power or number)

Verb

• decrease in phase
  • the moon is waning
    

• become smaller
  • Interest in his novels waned
    

• grow smaller
  • Interest in the project waned
    

Related words

• Synonyms: 
  ebb , ebbing , decline , go down
• Antonyms: 
  wax , full , mount , climb , rise