Origin of "Blackmail"?

What is the origin of this term? And, is it technically different than extortion? If so, what is the subtle difference? (I ask because the DC sniper is up on extortion charges for demanding money to stop the sniper shootings. Isn’t that blackmail?) Just a WAG: A person is blackmailed; organizations are extorted?

And, does mail come in any other colors? - Jinx

It is Scottish, as are most innovations.

It was a tribute paid by lowland farmers for protection against highland raids. It was, naturally, paid to those clans most likely to initiate a raid.

The “mail” part comes from an old English word for rent, and the “black” part may be because it was usually paid in goods or produce rather than coins or “white money.”

Balckmail usually is a type of extortion wherein the demands for money are based upon a threat to reveal something the victim would prefer to keep secret.