A guileless person behaves in an honest, open way. They are not hiding a plan, and they are not trying to trick you. A guileless smile is the kind that has nothing sitting behind it. The word is kinder than simple and clearer than innocent, though people sometimes use it with a little pity, as if this openness might get the person hurt. You will meet it in stories and in careful description of faces and manners; it is not street slang. Though actually, students often mix this up with guiltless. Guileless means without guile — no cunning. Guiltless means without guilt — not responsible for a wrong. They look like cousins, but they point at different things.