button up verb 4/ˈbʌtənˌʌp/ noun 1forms 4 verb4 •To fasten with a button or buttons.Button up your shirt cuff. It has come undone. •To fasten all the buttons on a coat, or similar item of clothing, to keep warm.Button up well. It's freezing outside today. •To conclude; to finalize; to put the finishing touches (on).It's time to button up the meeting. •(US, slang) To seal off (a military vehicle or facility).Once buttoned up, NORAD's operation center can survive for more than 30 days without aid from the outside world. — 1996 button-up /ˈbʌtənˌʌp/ noun1 •A shirt fastened by a vertical column of buttons at the front. formsbuttoned up · buttoning up · buttons up · button-ups