mid-15c., from Late Latin immersionem (nominative immersio), noun of action from past participle stem of immergere, from assimilated form of in- "into, in, on, upon" (see in-(2)) + Latin mergere "plunge, dip" (see merge). Meaning "absorption in some interest or situation" is from 1640s. As a method of teaching a foreign language, it is from 1965, trademarked by the Berlitz company.