The story
From Pluto + -ism, after the classical ruler of the underworld.
Etymology from Wiktionary, CC BY-SA 4.0.
plutonism
Today it means: The old geological theory that the rocks forming the Earth were formed in fire by volcanic activity, with a continuing gradual process of weathering and erosion, then deposited on the sea bed, re-formed into layers of sedimentary rock by heat and pressure, and raised again. Full definition →