Answer:
A dragon's tooth in a mortal's hand, I kill, I maim, I divide the land.
It is a sound of empty, speak and it'll talk back plenty. But all the more you yack, you'll get the same words back.
Tall in the morning, short at noon, gone at night. But I'll be back soon.
The man who made it didn't need it. The man who bought it didn't use it. The man who used it didn't want it.
I am nothing but holes tied to holes, yet am strong as iron.
My days are numbered. What am I?