Silent mind means to keep quiet temporarily. It is simply a suppression of the objects in the mind. It can happen many times, but it will not last.

Still mind is also temporary. Meditation or concentration can result in still mind. It is like a flame of a candle. When there is no breeze, the flame will be still. When wind comes, the candle will flicker and go out.

Still mind will be blown away as soon as it encounters the wind of another thought....