A weakening or decline in strength, power, ability, or vigor; deterioration (physical, economic, influence, etc.).
年を取ると体力の衰えを感じることが多い。
As you get older, you often feel a decline in physical strength.
景気の衰えが続き、失業率が上がった。
The economy's decline continued, and the unemployment rate rose.
長年の無関心が彼の影響力の衰えにつながった。
Years of indifference led to a decline in his influence.