BLACKMAIL, a term, in English law, used in three special meanings, at different times. The usual derivation of the second half of the word is from Norman Fr. maille (medalia; cf. "medal"), small copper coin; the New English Dictionary derives from "mail" (q.v.), meaning rent or tribute. (1) The primary meaning of "blackmail" was rent paid in labour, grain or baser metal (i.e. money other than sterling money), called reditus nigri, in contradistinction to rent paid in silver or white money (mailles blanches). (2) In the northern counties of England (Northumberland, Westmorland and the bishopric of Durham) it signified a tribute in money, corn, cattle or other consideration exacted from farmers and small owners by freebooters in return for immunity from robbers or moss-troopers. By a statute of 1601 it was made a felony without benefit of clergy to receive or pay such tribute, but the practice lingered until the union of England and Scotland in 1707. (3) The word now signifies extortion of money or property by threats of libel, presecution, exposure, etc. See such headings as Coercion, Conspiracy, Extortion, and authorities quoted under Criminal Law.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)