unbutton

verb (used with object)

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.

verb (used without object)

4. to unfasten a button or one’s buttons.

verb

1. to undo by unfastening (the buttons) of (a garment)
2. informal to release or relax (oneself, tension, etc)

v.early 14c., from un- (2) “opposite of” + button (v.). Related: Unbuttoned; unbuttoning.