I am interested, how would you say "motor oil" (the one that you put in your car engine) in Latin? Would it be "oleum" or "unguentum" or maybe something else?

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Rock oils, now called by the modern Greek-Latin word, petroleum, were in ancient times called bitumen by the Romans:

Babylone lacus amplissima magnitudine, qui limne asphaltitis appellatur, habet supra natans liquidum bitumen; quo bitumine et latere testaceo structum murum Sameramis circumdedit Babylonem. ("At Babylon there is a lake of wide extent which is called the Asphalt Lake, with liquid bitumen floating on it. Semiramis built a wall round Babylon of this bitumen and burnt-brick.") --Vitruvius

oleum itself is the oil of pressed olives. unguen refers properly to grease, but is also used when speaking of lubricating oils (Cato On Agriculture 146.2). The verb for oiling something is ungo. If you do not like the term petroleum, you could coin a term like motoroleum or motorileum or maybe use unguen the same way.

  • I'd say bitumen had little to do with actual motor oil, the former being black and untuous (although it can be liquid when hot), while the latter is transparent/translucent and definitely not black unless it's already burned. I'm not saying that you said they were the same, but the answer reads as if your proposed word for "motor oil" was bitumen (even after reading the last paraghraph).
    – walen
    Nov 21, 2023 at 12:43
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    @walen The modern idea of bitumen differs from the sense of the Roman word. Nov 21, 2023 at 13:25
  • In Spanish, bitumen means "Derived from tar, black and amorphous, which softens with heat and is used as waterproofing and paving" and we can trace this meaning all the way back to Alfonso X the Wise (1200s), who was way closer to Vitruvius' Latin than we'll ever be. And Vitruvius's bitumen was floating in Asphalt Lake and it was also used for construction. I may not understand what "bitumen" means in today's English, but I'm 100% sure it meant exactly the same for Vitruvius @ 30 BC than for me today -- and it has nothing to do with motor oil.
    – walen
    Nov 22, 2023 at 10:18
  • Your (indirect) proposal of just using petroleum or unguen, or making a new word like motoroleum, they all seem like better options to me than focusing on bitumen. They would convey the idea of "lubrication" way better than bitumen and are also closer to what modern motor oil (which didn't exist in 30 BC btw) would look like.
    – walen
    Nov 22, 2023 at 10:24

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