adjective · lacking fresh air or feeling oppressed from being shut indoors

屋里太闷了，把窗户打开吧。

verb · to cover something tightly or seal it off to keep air out or steam in

先把锅盖上闷一会儿。

adjective, verb · feeling bored, gloomy, or melancholy

他整天关在家里，觉得很闷。

verb, adjective · sealed or tightly closed

由于窗户全都关着，屋子里感觉特别闷。