stagnate
To stop growing, changing, or making progress and stay stuck.
When something stagnates, it stops growing, developing, or making progress. Like water in a pond with no fresh stream flowing in, it just sits there, becoming still and lifeless.
A student's learning might stagnate if they stop challenging themselves with harder books or problems. A company stagnates when it stops innovating and keeps doing things the same old way while competitors race ahead. A friendship can stagnate when two people stop sharing new experiences or having real conversations.
Picture the difference between a rushing river, full of life and motion, and a stagnant pond where the water has stopped moving and algae grows thick on the surface. That stillness captures what stagnation feels like: stuck, unchanging, going nowhere.
Stagnation (the noun form) happens when growth stops. Economic stagnation means businesses aren't expanding and people aren't finding new jobs. A writer experiencing stagnation might find themselves unable to develop new ideas or improve their craft.
The opposite of stagnating is progressing, growing, or advancing.