To unbutton means to unfasten or open something by releasing its buttons. When you unbutton your coat after coming inside from the cold, you slide each button back through its buttonhole to open the front. You might unbutton the top button of a shirt that feels too tight around your neck, or unbutton your jacket sleeves to roll them up on a warm day.

While buttoning closes something up, unbuttoning opens it back up. It's a simple but useful word that describes an everyday action we rarely think about.

Sometimes people use unbutton figuratively to mean relaxing or becoming less formal. After a long day at school, you might want to go home and unbutton (meaning to relax and be comfortable). When someone describes a dinner party as “unbuttoned,” they mean it felt casual and relaxed rather than stiff and formal.