Dull in a way that lowers your mood. Two strands are always twisted together: nothing interesting is happening, and that emptiness makes you feel a bit sad. Take away either strand and it's a different word — something merely uninteresting is 'boring', something merely sad is 'sad', but dreary is both at once. It goes most naturally with weather and places: a dreary November day, a dreary little town, dreary grey offices, a dreary hotel room. It also goes with work, tasks, and speeches when they drag on with nothing to hold you: 'a dreary meeting', 'the dreary business of filling in forms'. Applied to a person it's harsh — 'he's dreary' means he drains the life out of a room, which is a real criticism, not a light one. It's mildly formal and more written than spoken; in conversation a Taiwanese student is safer with 'depressing' or 'really dull'. Old poetry uses it to mean straightforwardly sad or gloomy, without the boredom part, so if you meet it in a nineteenth-century poem read it as 'bleak'.