verb (used with object)
to free (buttons) from buttonholes; unfasten or undo.
to unfasten by or as if by unbuttoning: to unbutton a jacket.
to disclose (one's feelings, thoughts, etc.) after deliberate or prolonged silence.
verb (used without object)
to unfasten a button or one's buttons.
Origin: 1275–1325; Middle English unbotenen.