Answer:
My voice is tender, my waist is slender and I'm often invited to play. Yet wherever I go, I must take my bow or else I have nothing to say.
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around
I am two-faced but bear only one. I have no legs but travel widely. Men spill much blood over me. Kings leave their imprint on me. I have greatest power when given away, yet lust for me keeps me locked away.
What is that you will break everytime you name it?
By the way, what never moves, wears shoes, sandals and boots, but has no feet?
What is so fragile that saying its name breaks it?