late 14c., "indestructible, unable to be loosened," also figuratively, of problems, etc., "incapable of being solved or explained," from Old French insoluble or directly from Latin insolubilis "that cannot be loosened," from in- "not" (see in- (1)) + solubilis "that can be loosened" (see soluble).
It was a tacit conviction of the learned during the Middle Ages that no such thing as an insoluble question existed. There might be matters that presented serious difficulties, but if you could lay them before the right man -- some Arab in Spain, for instance, omniscient by reason of studies into the details of which it was better not to inquire -- he would give you a conclusive answer. The real trouble was only to find your man. [Gertrude Bell, "The Desert and the Sown," 1907]
Meaning "incapable of being dissolved in a liquid" is from 1713.
"a mixture of liquids insoluble in one another, where one is suspended in the other in the form of minute globules," 1610s, from French émulsion (16c.), from Modern Latin emulsionem (nominative emulsio), noun of action from past participle stem of emulgere "to milk out," from assimilated form of ex "out" (see ex-) + mulgere "to milk" (from PIE root *melg- "to rub off; to milk"). The fat (butter) in milk is the classic example of an emulsion, drops of one liquid dispersed throughout another. Sense in photography is by 1840.
late 14c., probleme, "a difficult question proposed for discussion or solution; a riddle; a scientific topic for investigation," from Old French problème (14c.) and directly from Latin problema, from Greek problēma "a task, that which is proposed, a question;" also "anything projecting, headland, promontory; fence, barrier;" also "a problem in geometry," literally "thing put forward," from proballein "propose," from pro "forward" (from PIE root *per- (1) "forward") + ballein "to throw" (from PIE root *gwele- "to throw, reach").
The meaning "a difficulty" is mid-15c. Mathematical sense of "proposition requiring some operation to be performed" is from 1560s in English. Problem child, one in which problems of a personal or social character are manifested, is recorded by 1916. Phrase _______ problem in reference to a persistent and seemingly insoluble difficulty is attested from at least 1882, in Jewish problem. Response no problem "that is acceptable; that can be done without difficulty" is recorded from 1968.
late 12c., "olive oil," from Anglo-French and Old North French olie, from Old French oile, uile "oil" (12c., Modern French huile), from Latin oleum "oil, olive oil" (source of Spanish, Italian olio), from Greek elaion "olive tree," from elaia (see olive).
Nearly all the European languages' words for "oil" (Croatian ulje, Polish olej, Hungarian olaj, Albanian uli, Lithuanian alejus, etc.) are from the Greek word; the Germanic (except Gothic) and Celtic one coming from Greek via Latin: Old English æle, Dutch olie, German Öl, Welsh olew, Gaelic uill, etc.
In English it meant "olive oil" exclusively till c. 1300, when the word began to be extended to any fatty, greasy liquid substance (usually flammable and insoluble in water). Often especially "oil as burned in a lamp to afford light" (as in midnight oil, symbolizing late work). Use for "petroleum" is recorded from 1520s but not common until 19c.
The artist's oils (1660s), short for oil-color (1530s), are paints made by grinding pigment in oil. Oil-painting is attested from 1782. The ocean-going oil-tanker is from 1900; oil-spill is from 1970. As a condiment, oil and vinegar is attested from 1620s. The figurative expression pour oil upon the waters "appease strife or disturbance" is by 1840, from an ancient trick of sailors.
Another historical illustration which involves monolayers, was when sailors poured oil on the sea in order to calm 'troubled waters' and so protect their ship. This worked by wave damping or, more precisely, by preventing small ripples from forming in the first place so that the wind could have no effect on them. [J. Lyklema, "Fundamentals of Interface and Colloid Science," Academic Press, 2000]
The phenomenon depends on what are called Marangoni effects; Benjamin Franklin experimented with it in 1765.