plural declines
1 : the process of becoming worse in condition or quality
[noncount]
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
[count]
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.
[noncount]
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.