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early 15c., "withdrawal, removal" (originally of noxious substances from the body), from Latin subductionem (nominative subductio), noun of action from past participle stem of subducere (see subduce). Geological sense is attested from 1970, from French (1951).
A geologic process in which one edge of one lithospheric plate is forced below the edge of another. The denser of the two plates sinks beneath the other. As it descends, the plate often generates seismic and volcanic activity (from melting and upward migration of magma) in the overriding plate. Compare obduction.