stagnant

/ˈstæɡnənt/
adjective
  1. Not flowing or moving, especially of water or air; often becoming dirty or smelly as a result.
    • The pond became stagnant after the stream was blocked.
    • We had to open the windows to let out the stagnant air in the room.
    • Mosquitoes breed in stagnant water, so you should empty any containers in your yard.
  2. Not changing or developing; inactive or dull.
    • The company's sales were stagnant, neither growing nor shrinking.
    • The economy has been stagnant for years, with no new jobs being created.
    • His career felt stagnant, so he decided to go back to school.