What is the origin of the idiom "under one's thumb" and when to use it?

The origin of the idiom "under one's thumb" is not definitively known, but it has been in use since the 17th century. The phrase likely comes from the image of someone being under the physical control of another person, with the thumb representing dominance and control. The thumb is a powerful digit that can exert pressure and control over objects, and by extension, over people. The phrase may have originated from physical gestures or actions where someone literally presses their thumb upon another person to assert dominance or control.