What is the difference between a trait and a habit?

A habit is a behaviour. It's something you do, all the time (and have a hard time not doing). A trait is part of your personality. It's something you are, all the time (or most of it anyway). For example, smoking is something you do, so it can be a habit, if you do it all the time. But being cheerful, or cheap or suspicious is not something you do, but is part of how you are. Those are traits.