1 : the process of becoming worse in condition or quality
a period of economic decline
He says that American industry is in a state of decline.
There was a general feeling that the country was in decline. [=was becoming less powerful, wealthy, etc.]
The town fell/went into decline after the factory closed down.
[count] — usually singular
He has experienced a decline in health.
the decline and fall of the Roman empire
The company's products suffered a decline in quality.
a gradual physical/mental decline
2 : a change to a lower number or amount
The economy experienced a decline of two million jobs.
We saw a sharp/steep decline in sales this month.
Declines led advances at the end of the trading day.
There was some decline in stock prices at the end of the trading session.
on the decline
: becoming worse in condition or less in size, amount, number, etc. : declining
His health is on the decline.
Sales are on the decline.