Olives, deliberately planted and tended for thousands of years, are intimately tied to the early diets of ancient humans, who carefully cultivated them wherever they roamed, so much so that a plant with Afro-Asiatic ancestry is now grown even in Washington state. It's no small thing, that, and it marks the importance of the olive tree in human history, given that the plant is used not only for the fruit (the olive), but for the oil, pressed from the fruit, the leaves, and even the wood. English, etymologically speaking, obtained the word olive via Old French, olive, from Latin oliva, "olive, olive tree," from Greek elaia "olive tree, olive." Elaia is most likely derived from one of the Aegean languages, possibly Cretan, or Minoan, since we also see ewi "oil" in Armenian. From roughly the 14th century on in Middle English, we routinely see olive used for the tree, and the fruit of the tree. Trees are closely tied to human migrations across the continent of Europe because humans took the plants that were most important for their survival, based on their uses for wood, oil, food and religion, with them, as they moved from the fertile crescent around the Tigris and Euphrates, across Asia and Europe, and, centuries later, to the New World.

Olives are so closely tied to the early diets of Europe, the Mediterranean and the Middle East, that the word oil, meaning "Any of numerous mineral, vegetable, and synthetic substances and animal and vegetable fats that are generally slippery, combustible, viscous, liquid or liquefiable at room temperatures, soluble in various organic solvents such as ether but not in water, and used in a great variety of products, especially lubricants and fuels" (AHD) that the word for "oil" in a large number of Indo-European and Semitic languages derives from the word for olive. In English, for instance, we see already by 1175 olie, oile "olive oil" from Anglo-Norman and Norman French olie, and huile in 12th century French, from Latin oelum "oil, olive oil," Greek elaion "Olive tree," from elaia "olive." In Middle English, olie always meant "olive oil" until ca. 1300, when olie began to be used for any fatty, greasy substance, even those associated with fossil fuels, or petroleum. Or food, in the creation of oleo in the nineteenth century, and the subsequent increase in use during World War II as margarine began to used at home instead of butter.

Oleo, short for oleomargarine, derives from "oil" via Latin oelum. Petroleum entered English via Middle Latin as a compound ca. 1520–30. Petroleum derives form Latin petr (derived from Greek pétra), "rock" + Latin oleum.

And it all goes back to a simple olive tree, potentially living for thousands of years.