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.
