means Molten or solidified rock that has erupted from a volcano onto Earth's surface.

from From Italian 'lava,' which likely came from the Neapolitan dialect describing a stream of rain or debris washing down a slope — fittingly used by Vesuvius's neighbors for the rivers of molten rock that did the same. It traces back to Latin 'labes,' a falling or sliding (related to 'labi,' to slip), so the word literally remembers the way the stuff flows downhill rather than its heat.