What is the origin of the word Undertaker?

Answer 1

Who will undertake to dispose of this body?
In the ancient world, who ever answered "yes" to that question was the undertaker. The name simply stuck once this became a profession, not a voluntary civic activity.

Answer 2

Originally, undertaker referred to a person who under takes any kind of task. First recorded about 1400, the word is derived from the verb undertake, "to take upon oneself."
Around 1700, undertaker began to be specifically applied to those who prepare the dead for the grave.

Answer 3

Because they TAKE you UNDER the ground!