Blackmail
mid 16th century (denoting protection money levied by Scottish chiefs): from black + obsolete mail ‘tribute, rent’, from Old Norse mál ‘speech, agreement’.
wiktionary
From black + mail(“a piece of money”). Compare Middle English blak rente(“a type of blackmail levied by Irish chieftains”).
The word is variously derived from the tribute paid by English and Scottish border dwellers to Border Reivers in return for immunity from raids and other harassment. This tribute was paid in goods or labour, in Latinreditus nigri "blackmail"; the opposite is blanche firmes or reditus albi "white rent", denoting payment by silver. Alternatively, McKay derives it from two Scottish Gaelic words blàthaich, pronounced (the th silent) bl-aich, "to protect" and màl(“tribute, payment”). He notes that the practice was common in the Highlands of Scotland as well as the Borders.
More likely, from black (adj.) + Middle English mal, male, maile(“a payment, rent, tribute”), from Old English māl(“speech, contract, agreement, lawsuit, terms, bargaining”), from Old Norse mál(“agreement, speech, lawsuit”); related to Old English mæðel "meeting, council," mæl "speech," Gothic 𐌼𐌰𐌸𐌻( maþl) "meeting place," from Proto-Germanic *maþlą, from PIE *mod- "to meet, assemble" (see meet (v.)). From the practice of freebooting clan chieftains who ran protection rackets against Scottish farmers. Black from the evil of the practice. Expanded c.1826 to any type of extortion money. Compare silver mail "rent paid in money" (1590s); buttock-mail (Scottish, 1530s) "fine imposed for fornication."
etymonline
blackmail (n.)
1550s, "tribute paid to men allied with criminals as protection against pillage, etc.," from black (adj.) + Middle English male "rent, tribute," from Old English mal "lawsuit, terms, bargaining, agreement," from Old Norse mal "speech, agreement;" related to Old English mæðel "meeting, council," mæl "speech," Gothic maþl "meeting place," from Proto-Germanic *mathla-, from PIE *mod- "to meet, assemble" (see meet (v.)).
The word comes from the freebooting clan chieftains who ran protection rackets against farmers in Scotland and northern England. The custom persisted until mid-18c. Black from the evil of the practice. The sense expanded by 1826 to mean any extortion by means of intimidation, especially by threat of exposure or scandal. Compare silver mail "rent paid in money" (1590s); buttock-mail (Scottish, 1530s) "fine imposed for fornication."
blackmail (v.)
"to extort money or goods from by intimidation or threat," especially of exposure of some wrong-doing, 1852, from blackmail (n.). Related: Blackmailed; blackmailing.
