waning

(noun) a gradual decrease in magnitude or extent. Examples: "The waning of his enthusiasm was obvious." "The waxing and waning of the moon."

(verb) grow smaller. Synonyms: decline, go down, wane. Example: "Interest in the project waned."

(verb) become smaller. Synonyms: wane. Example: "Interest in his novels waned."

(verb) decrease in phase. Synonyms: wane. Example: "The moon is waning."

(adj) (of the Moon) pertaining to the period during which the visible surface of the moon decreases. Synonyms: waning (vs. waxing). Example: "After full moon comes the waning moon."