An overreaction is the too-big answer itself: the extra anger, the panic, the heavy punishment, or the sudden rule that the problem did not really need. It is the noun that sits next to the verb overreact. Offices, news, and families all use it — “That was an overreaction.” Doctors sometimes use it when a body answers too strongly, but everyday talk is almost always about feelings and behaviour. Though actually, calling something an overreaction is already a judgement. You are saying the other person’s size of feeling was wrong, so say it kindly, or be ready for an argument. One moment of overreacting is a verb; the thing they did, or the pattern of it, is the overreaction.