means The geological process by which one tectonic plate slides beneath another and sinks into the mantle, often building mountains, volcanoes, and earthquakes along the way.

from From Latin 'subducere,' to lead or draw away from below — 'sub-' (under) plus 'ducere' (to lead, the same root behind 'conduct,' 'duke,' and 'aqueduct'). Long used in English for the simple act of taking away or withdrawing something underneath, the word was drafted into geology in the 20th century as plate tectonics took shape, when scientists needed a name for one slab being led downward beneath its neighbor.