Stuffiness is that uncomfortable, stale feeling in a room where the air seems thick and hard to breathe. When a classroom has been closed up all night with the windows shut, you notice the stuffiness the moment you walk in: the air feels heavy, warm, and used up. Opening windows and letting fresh air flow through gets rid of stuffiness.

The word can also describe people who are overly formal, rigid, and concerned with rules and propriety. A stuffy person might insist everyone dress formally for a casual backyard barbecue, or refuse to laugh at a harmless joke because they think it's undignified. Someone described as stuffy often cares more about appearances and traditions than about having fun or being flexible. A stuffy adult might say things like “Children should be seen and not heard” or correct your grammar at the dinner table.

You might encounter stuffiness in old buildings, boring meetings, or social situations where everyone seems too worried about proper behavior to relax and be themselves.