term:

Blackmail

blackmail n

[originally, payment extorted from farmers in Scotland and northern England, from black + dialectal mail payment, rent]
: extortion or coercion by often written threats esp. of public exposure, physical harm, or criminal prosecution
blackmail vt

black·mail·er [-mā-lər]
n

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.