Etymology
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fornication (n.)

c. 1300, from Old French fornicacion "fornication, lewdness; prostitution; idolatry" (12c.), from Late Latin fornicationem (nominative fornicatio), noun of action from past-participle stem of fornicari "to fornicate," from Latin fornix (genitive fornicis) "brothel" (Juvenal, Horace), originally "arch, vaulted chamber, a vaulted opening, a covered way," probably an extension, based on appearance, from a source akin to fornus "brick oven of arched or domed shape" (from PIE root *gwher- "to heat, warm"). Strictly, "voluntary sex between an unmarried man and an unmarried woman;" extended in the Bible to adultery. The sense extension in Latin is perhaps because Roman prostitutes commonly solicited from under the arches of certain buildings.

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fornicator (n.)
late 14c., from Late Latin fornicator, agent noun from fornicat-, stem of fornicari "to fornicate" (see fornication). Of the fem. forms, fornicatrice is c. 1500, fornicatrix 1580s, fornicatress 1590s.
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*gwher- 

Proto-Indo-European root meaning "to heat, warm."

It forms all or part of: brand; brandish; brandy; brimstone; brindled; forceps; Fornax; fornicate; fornication; fornix; furnace; hypothermia; thermal; thermo-; Thermopylae; Thermos.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit gharmah "heat;" Old Persian Garmapada-, name of the fourth month, corresponding to June/July, from garma- "heat;" Hittite war- "to burn;" Armenian jerm "warm;" Greek thermos "warm;" Latin formus "warm," fornax "oven;" Old Irish fogeir "heated;" Old English bærnan "to kindle."

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skulduddery (n.)
also sculduddery, "fornication," 1713; see skulduggery.
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bastardy (n.)
early 14c., "condition of illegitimacy," from Anglo-French and Old French bastardie, from bastard (see bastard). As "begetting of bastards, fornication" from 1570s.
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fornicate (v.)
1550s, "have illicit sexual intercourse" (said of an unmarried person), from Late Latin fornicatus, past participle of fornicari "to fornicate," from Latin fornix (genitive fornicis) "brothel" (Juvenal, Horace), originally "arch, vaulted chamber, a vaulted opening, a covered way," probably an extension, based on appearance, from a source akin to fornus "brick oven of arched or domed shape" (from PIE root *gwher- "to heat, warm"). Perhaps in some cases a back-formation from fornication. Related: Fornicated; fornicating.
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jollity (n.)
early 14c., jolyfte, iolite, "merrymaking, revelry," also "agreeableness, attractiveness, beauty, elegance;" from Old French jolivete "gaity, cheerfulness; amorous passion; life of pleasure," from jolif "festive, merry" (see jolly).

From late 14c. as "lightheartedness, cheerfulness." A word with more senses in Middle and early Modern English than recently: "sexual pleasure or indulgence, lust" (mid-14c.); "insolent presumptuousness, impudence" (mid-14c.); "vigor, strength" (mid-14c.); "love; a love affair" (c. 1300, hence in jollity "by fornication, out of wedlock"); "gallantry" (1530s); "state of splendor" (1540s).
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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."
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