Malodorous means smelling unpleasant. It is a formal, slightly stiff or jokey-high word for stinky. You meet it in writing more than in talk: a malodorous drain, malodorous cheese, a malodorous cupboard. In everyday speech people say smelly, stinky, or “it smells bad.” It does not tell you what kind of bad smell — only that the smell is unwelcome. Though actually, odorous on its own can mean “having a smell,” not always a bad one; the mal- is what makes it bad.