Cases of word usage

1) a joint on which a lid, door or gate turns or swings; the central principle on which something depends (hinge)

2) a stone at the top of an arch locking the others into position; the central principle on which an argument, idea etc depends (keystone)

3) a person who is put to death or caused to suffer greatly for the sake of a great cause, religious belief or principle (martyr)

4) (the belief in) the principle that war should and could be abolished (pacifism)

5) a long, flat piece of wood; a basic principle in a political policy (plank)