unbutton
verbUK /ʌnˈbʌt.ən/
US /ʌnˈbʌt.ən/
To open the buttons on your clothes.
She had to unbutton her coat because it was too warm inside.
RELATED WORDS
OTHER MEANINGS
2. To release or let go of something held tightly, like a feeling or a plan.
He unbuttoned his anger and finally told the truth.
3. To become open by itself, as when buttons come undone.
The old jacket unbuttoned in the wind.
4. To relax and become less formal in behavior.
After work, he unbuttoned and joked with his friends.