oil (n.)

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.

"to smear or rub with oil or ointment," mid-15c., oilen, from oil (n.). Later especially "to lubricate (machinery)." Related: Oiled; oiling. An Old English verb in this sense was besmyrian.