The adjective composed describes someone who is calm and shows no nervousness or agitation. You may be very upset about your brother’s unkind remark, but your composed face doesn’t give away your feelings.
If you’re composed, that means you're free of emotion or nervousness — or at least you look that way. Composed typically describes an outward appearance, so you could be angry on the inside but still maintain a composed manner that hides what you’re really feeling. You’ll often hear the word used to describe someone who can keep everything under control during times of stress. You probably look composed even when you’re stressing out over your calculus exam.