/un but"n/ , v.t.
1. to free (buttons) from buttonholes; unfasten or undo.
2. to unfasten by or as if by unbuttoning: to unbutton a jacket.
3. to disclose (one's feelings, thoughts, etc.) after deliberate or prolonged silence.
v.i.
4. to unfasten a button or one's buttons.
[ 1275-1325; ME unbotenen. See UN- 2 , BUTTON ]