When someone is guarded, they do not give you much information and they do not show their feelings. They may be polite, even warm on the surface, but they keep a wall up. You hear it about people and about the way they speak: a guarded answer, a guarded look, a guarded smile. It comes from the idea of a guard — as if your thoughts were a place that needed watching. Though actually, it is not the same as shy. A shy person may want to talk and find it hard. A guarded person has decided not to give you much, often because they do not quite trust the room. Newspapers also like “guarded optimism” or a “guarded welcome”: people are a little hopeful, but they will not say they are sure. The first meaning students meet is a soldier’s guard; this meaning is the feeling-and-talk one.