To open (something) by undoing its buttons.
To come open by having its buttons unfastened.
To loosen or undo (something that entangles, fastens, holds, or interlocks).
To free (someone or something) from a constraint; (figuratively) to release (something which has been suppressed, such as emotions or objectionable things).
To relax or slacken (something that clasps or grips, such as the arms or hands).
To become loose or come off.
To free from a constraint.