Nouns

(n)decline, diminutionchange toward something smaller or lower
(n)decline, declinationa condition inferior to an earlier condition; a gradual falling off from a better state; decline
(n)decay, declinea gradual decrease; as of stored charge or current

Verbs

(v)worsen, declinegrow worse“Conditions in the slum worsened”
(v)refuse, reject, pass up, turn down, declinenot accept as true“He refused to accept what she said”
(v)refuse, declineshow unwillingness towards“he declined to join the group on a hike”
(v)decline, go down, wanegrow smaller“Interest in the project waned”
(v)declinego down“The roof declines here”
(v)decline, slump, correctfall in value“the stock market corrected”, “prices slumped”
(v)declineinflect for number, gender, case, etc.“in many languages, speakers decline nouns, pronouns, and adjectives”