UNBUTTON Meaning of UNBUTTON in English un ‧ but ‧ ton /ʌnˈbʌtn/ BrE AmE verb [transitive] to undo the buttons on a piece of clothing OPP button up :He took off his sweater and unbuttoned his shirt. Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012