Stagnant describes water that isn't flowing or moving, sitting still in one place for so long that it becomes unhealthy. A stagnant pond has no fresh water flowing through it, so algae grows thick on the surface, mosquitoes breed in it, and it develops an unpleasant smell. Compare this to a flowing stream, where the constant movement keeps the water clean and fresh.

The word also describes situations where nothing is changing, growing, or improving. A stagnant economy isn't creating new jobs or opportunities. A student whose skills remain stagnant isn't learning or developing: they're stuck at the same level month after month. When a friendship becomes stagnant, you might find yourselves doing the same boring activities without trying anything new or having meaningful conversations.

The connection between these meanings makes sense: just like still water becomes lifeless and unhealthy, situations that don't move forward tend to lose their vitality. When something is stagnant, it needs a change, some kind of movement or fresh input to become healthy and productive again. The noun form is stagnation, describing that state of unhealthy stillness or lack of progress.