immersion (n.)

c. 1500, from Late Latin immersionem (nominative immersio), noun of action from past participle stem of immergere "to plunge in, dip into, sink, submerge," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + Latin mergere "plunge, dip" (see merge). Meaning "absorption in some interest or situation" is from 1640s. As a method of teaching a foreign language, 1965, trademarked by the Berlitz company.