/ ɪˈmɜːʃn; NAmE ɪˈmɜːrʃn; -ʒn/ noun [ U ]
1.
immersion (in sth) the act of putting sb/sth into a liquid so that they or it are completely covered; the state of being completely covered by a liquid :
Immersion in cold water resulted in rapid loss of heat.
baptism by total immersion (= putting the whole body underwater)
2.
immersion (in sth) the state of being completely involved in sth :
his long immersion in politics
a two-week immersion course in French (= in which the student will hear and use only French)
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WORD ORIGIN
late 15th cent.: from late Latin immersio(n-) , from immergere dip into, from in- in + mergere to dip.