stagnate
Definitions
To cease to flow or move, typically becoming foul or stale.
To stop developing, progressing, or advancing; to become inactive or dull.
Examples
If the economy continues to stagnate, many small businesses will be forced to close.
Without new ideas and creative challenges, his professional growth began to stagnate.
The water in the pond started to stagnate because there was no flow to keep it fresh.