石油
せきゆ · sekiyu · JLPT N3 · noun
oil
🛢️⛽ 石油 = stone + oil: oil that comes out of rock
石 (seki) means stone or rock, and 油 (yu) means oil. Petroleum is literally rock oil, which is also where the English word comes from: Latin petra (rock) + oleum (oil).
油 — water radical 氵 + 由 (yóu, phonetic)
油 is a phono-semantic compound. The 氵 radical signals a liquid, while 由 supplies the sound. Originally referring to a river name, it was extended to mean oil or fat — any thick, flowing liquid — which became its dominant modern sense.