Etymology
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subtlety (n.)
c. 1300, sotilte, "skill, ingenuity," from Old French sotilte "skillfulness, cunning" (Modern French subtilité), from Latin subtilitatem (nominative subtilitas) "fineness; simplicity, slenderness," noun of quality from subtilis "fine, thin, delicate" (see subtle). From late 14c. as "cleverness, shrewdness; trickery, guile, craftiness," also "thinness, slenderness, smallness; rarity." The -b- begins to appear late 14c. in English, in imitation of Latin.
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subtility (n.)
late 14c., "acuteness, skill, cunning," alteration of subtlety (q.v.) on model of subtile, or else from Old French subtilite, from Latin subtilitas "fineness, simplicity."
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finesse (n.)

1520s, "fineness" (obsolete); 1530s, "artifice, delicate stratagem," from French finesse "fineness, subtlety," from Old French fin "subtle, delicate" (see fine (adj.)).

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quillet (n.)

"a quibble, a nicety or subtlety," 1580s, obsolete, probably a corruption or contraction of Latin quidlibet "what you please," from quid "anything," neuter of indefinite pronoun quis "somebody, someone or other" (from PIE root *kwo-, stem of relative and interrogative pronouns) + libet "it pleases" (from PIE root *leubh- "to care, desire, love").

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quodlibet (n.)

"a nicety, subtlety," late 14c., "a question proposed in a university for disputation, on any academic topic," from Medieval Latin, literally "what you will, what you please," from quod "what," neuter of qui (from PIE root *kwo-, stem of relative and interrogative pronouns) + libet "it pleases" (from PIE root *leubh- "to care, desire, love"). Sense evolution is via the notion of "a scholastic argumentation" upon a subject chosen at will (but usually theological). Related: Quodlibetarian; quodlibetic; quodlibetical.

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chicanery (n.)

c. 1610s, "legal quibbling, sophistry, mean or petty tricks," from French chicanerie "trickery," from chicaner "to pettifog, quibble" (15c.), which is of unknown origin, perhaps from Middle Low German schikken "to arrange, bring about," or from the name of a golf-like game once played in Languedoc. Also compare French chic "small, little," as a noun "a small piece; finesse, subtlety." Thornton's "American Glossary" has shecoonery (1845), which it describes as probably a corruption of chicanery.

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chic (n.)

1856, "style in fine art, artistic skill, faculty of producing excellence rapidly and easily," from French chic "stylishness" (19c.), originally "subtlety" (16c.), which is of unknown origin. Perhaps [Klein] it is related to German Schick, Geschick "tact, skill, aptness," from Middle Low German schikken "arrange appropriately," or Middle High German schicken "to arrange, set in order." Or perhaps it is from French chicane, from chicanerie "trickery" (see chicanery).

Meaning "Parisian elegance and stylishness combined with originality" is by 1882 (Pall Mall Gazette, Sept. 6, 1888, uses the word in a concert review and pauses to define it as "an untranslatable word, denoting an indispensable quality"). As an adjective, in reference to persons, "stylish," 1879 in English. "Not so used in F[rench]" [OED].

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compass (n.)

c. 1300, "space, area, extent, circumference," from Old French compas "circle, radius; size, extent; pair of compasses" (12c.), from compasser "to go around, measure (with a compass); divide equally," from Vulgar Latin *compassare "to pace out," from Latin com "with, together" (see com-) + passus "a step" (from PIE root *pete- "to spread").

The mathematical instrument for describing circles was so called in English from mid-14c. The mariners' directional tool (so called since early 15c.) took the name, perhaps, because it's round and has a point like the mathematical instrument.

Meaning "limits, boundary" is from 1550s. Sense of "range of notes which a given voice or instrument can produce" is from 1590s. 

The word is in most European languages, with a mathematical sense in Romance, a nautical sense in Germanic, and both in English. In Middle English it also could mean "ingenuity, subtlety, cunning." Also an adverb in Middle English: to go compass was "go in a circle, go around."

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brotherhood (n.)

14c., "fraternal relation, relationship between sons of the same father or mother," from brother + -hood; earlier was brotherhede (c. 1300), with ending as in maidenhead; and Old English had broþerrede, with ending as in kindred. The modern form of the word prevailed from 15c.

Originally "relationship of a brother," also "friendly companionship." Concrete sense of "an association of men for any purpose, a fraternity" is from mid-14c. in the Middle English word (later also "labor union," 1880s). Meaning "a class of individuals of the same kind" is from 1728. Meaning "community feeling uniting all humankind" is from 1784. Old English also had broðorscipe "brothership," broðorsibb "kinship of brothers."

What edge of subtlety canst thou suppose
Keen enough, wise and skilful as thou art,
To cut the link of brotherhood, by which
One common Maker bound me to the kind?
[Cowper, from "The Task," 1785]

***

Oh, the Protestants hate the Catholics,
And the Catholics hate the Protestants,
And the Hindus hate the Muslims,
And everybody hates the Jews.
[Tom Lehrer, "National Brotherhood Week" lyrics, 1965]
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doublethink (n.)

"power of holding two contradictory beliefs in one's mind simultaneously, and accepting both of them" (Orwell), 1948, coined by George Orwell in "Nineteen Eighty-Four," from double (adj.) + think.

To know and not to know, to be conscious of complete truthfulness while telling carefully constructed lies, to hold simultaneously two opinions which cancelled out, knowing them to be contradictory and believing in both of them, to use logic against logic, to repudiate morality while laying claim to it, to believe that democracy was impossible and that the Party was the guardian of democracy, to forget whatever it was necessary to forget, then to draw it back into memory again at the moment when it was needed, and then promptly to forget it again, and above all, to apply the same process to the process itself—that was the ultimate subtlety: consciously to induce unconsciousness, and then, once again, to become unconscious of the act of hypnosis you had just performed. Even to understand the word—doublethink—involved the use of doublethink. ["Nineteen Eighty-Four"]
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