Etymology
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unlikely (adj.)
late 14c., "not likely to occur," from un- (1) "not" + likely (adj.). Similar formation in Old Norse ulikligr, Middle Danish uligelig. Meaning "not likely to be true" is recorded from 1590s. Related: Unlikeliness; unlikelihood.
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unlikely (adv.)
mid-15c., "improbably," from un- (1) "not" + likely (adv.) (see likely (adj.)).
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mace (n.2)

"spice made from dry outer husk of nutmeg," late 14c., from Old French macis (in English taken as a plural and stripped of its -s), a word of uncertain origin, sometimes said to be a scribal error for Latin macir, the name of a red spicy bark from India, but OED finds this etymology unlikely.

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marijuana (n.)

a preparation of Cannabis sativa for use as an intoxicant, generally by smoking, 1918, altered by influence of Spanish proper name Maria Juana "Mary Jane" from mariguan (1894), from Mexican Spanish marihuana, which is of uncertain origin. As the plant was not native to Mexico, a native source for the word seems unlikely.

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inconvenient (adj.)

late 14c., "injurious, dangerous," also "absurd, illogical" (senses now obsolete), from Latin inconvenientem (nominative inconveniens) "unsuitable, not accordant, dissimilar," from in- "not, opposite of" (see in- (1)) + convenientem (see convenient). In early 15c., "inappropriate, unbecoming, unnatural;" also, of an accused person, "unlikely as a culprit, innocent." Sense of "troublesome, incommodious, awkward" is recorded from 1650s.

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algae (n.)
(plural), 1794, from alga (singular), 1550s, from Latin alga "seaweed," which is of uncertain origin. Perhaps connected to Latin ulva "grass-like or rush-like aquatic plant," or perhaps from a PIE root meaning "to putrefy, rot," but de Vaan considers this unlikely and suggests it might be a foreign loan-word.
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Tantalus 

Greek Tantalos, ancient mythical king of Phrygia, a name of uncertain origin, perhaps literally "the Bearer" or "the Sufferer," by dissimilation from *tal-talos, a reduplication of PIE root *tele- "to bear, carry, support" (see extol), in reference to his long endurance, but Watkins finds this "unlikely" and Beekes writes that "An IE interpretation is most improbable." Compare tantalize.

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long shot (n.)

also long-shot, in the figurative sense of "something unlikely," 1867, from long (adj.) + shot (n.). The notion is of a shot at a target from a great distance, thus difficult to make. The phrase by a long shot "by a considerable amount," frequently negative, is attested by 1830, American English colloquial. The cinematic sense of the noun phrase is from 1922. As an adjective by 1975.

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bistro (n.)
1906, from French bistro (1884), originally Parisian slang for "little wineshop or restaurant," which is of unknown origin. Commonly said to be from Russian bee-stra "quickly," picked up during the Allied occupation of Paris in 1815 after the defeat of Napoleon; but this, however quaint, is unlikely. Another guess is that it is from bistraud "a little shepherd," a word of the Poitou dialect, from biste "goat."
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heather (n.)
early 14c., hathir, from Old English *hæddre, Scottish or northern England dialect name for Calluna vulgaris, probably altered by heath, but real connection to that word is unlikely [Liberman, OED]. Perhaps originally Celtic. As a fem. proper name little used in U.S. before 1935, but a top-15 name for girls born there 1971-1989.
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