decline

verb

• 1 [no object] (typically of something regarded as good) become smaller, fewer, or less; decrease:the birth rate continued to decline
• diminish in strength or quality; deteriorate:her health began to decline (as adjective declining)declining industries

• 2 [with object] politely refuse (an invitation or offer):Caroline declined the coffee [with infinitive]:the company declined to comment

• 3 [no object] (especially of the sun) move downwards: the sun began to creep round to the west and to decline
• archaic bend down; droop: the wearisome creatures of the world declining to their rest

• 4 [with object] (in the grammar of Latin, Greek, and certain other languages) state the forms of (a noun, pronoun, or adjective) corresponding to case, number, and gender.

noun

• a gradual and continuous loss of strength, numbers, or value:a serious decline in bird numbers [mass noun]:a civilization in decline
• archaic the sun’s gradual setting: this Evening from the Sun’s decline arriv’d
• archaic a disease in which the bodily strength gradually fails, especially tuberculosis: he died at his brother’s of a deep decline