"an inexpressible something," French, literally "I do not know what."
[T]hey are troubled with the je-ne-scay-quoy, that faign themselves sick out of niceness but know not where their own grief lies, or what ayls them. [Thomas Blount, "Glossographia," 1656]
1927 as "phony remedy," American English, from the use of oil derived from the fat of snakes (especially the rattlesnake) as a folk remedy in the rural regions of the U.S. Snake oil in this sense is attested by 1858. It was a folk remedy for rheumatism and gout in Georgia, but a cure for deafness in rural Pennsylvania. Professional pharmacy journals began to condemn it early 20c., not because it was quackery but because products sold under the name had no real snake oil in them.
What is known as snake oil is usually a combination which is handed out by the dealer to satisfy the demand of some credulous customer. A genuine oil of course is that which is obtained by "trying out" the fat of a snake, usually the rattlesnake, and to preserve their faces druggists sometimes employ a small proportion of such oil in preparing the weird mixtures dispensed by them. [The Practical Druggist, July 1912]
sink to wash food, dishes, etc., 1824. Phrase everything but (or and) the kitchen sink is attested from 1944, from World War II armed forces slang, in reference to intense bombardment.
Out for blood, our Navy throws everything but the kitchen sink at Jap vessels, warships and transports alike. [Shell fuel advertisement, Life magazine, Jan. 24, 1944]
Earlier was everything but the kitchen stove (1919).
motto of the United States, being one nation formed by uniting several states, 1782, Latin, from e "out of" (see ex-); ablative plural of plus "more" (see plus (n.)); neuter of unus "one" (from PIE root *oi-no- "one, unique"). Not found in classical Latin, though a variant of the phrase appears in Virgil (color est e pluribus unum); the full phrase was the motto of the popular Gentleman's Magazine from 1731 into the 1750s.
mid-14c., also simply coat (mid-14c.); originally a tunic embroidered or painted with heraldic armorial bearings (worn over armor, etc); see coat (n.) + arm (n.2) and compare Old French cote a armer. Sense transferred in Middle English to the heraldic arms themselves. Hence turncoat, one who put his coat on inside-out to hide the badge of his loyalty (1550s).
1761, "any disabled person or thing;" especially Stock Exchange slang for "defaulter."
A lame duck is a man who cannot pay his differences, and is said to waddle off. [Thomas Love Peacock, "Gryll Grange," 1861]
Sometimes also in naval use for "an old, slow ship." Modern sense of "public official serving out term after an election" is recorded by 1863, American English. The quote attributed to President Lincoln ("[A] senator or representative out of business is a sort of lame duck. He has to be provided for") is from an anecdote of 1878.
It is well known to everybody who knows anything of its history, that this court [Court of Claims] was made a sort of retreat for lame duck politicians that got wounded and had to retreat before the face of popular condemnation. That is just exactly what it was for, a safe retreat for lame ducks; and it was so filled up; (etc.) [Sen. John P. Hale, New Hampshire, Congressional Globe, Jan. 12, 1863, p.271]