Answer:
A dragon's tooth in a mortal's hand, I kill, I maim, I divide the land.
What is never used unless it's in a tight place?
What has a single eye but cannot see?
My first master has four legs, my second master has two. My first I serve in life, my second I serve in death. Tough I am, yet soft beside. Against ladies cheeks I often reside.
My first is high, My second damp, My whole a tie, A writer's cramp
I am your mother's brother's only brother in law. Who am I?