n.1 the act or an instance of immersing; the process of being immersed.
2 baptism by immersing the whole person in water.
3 mental absorption.
4 Astron. the disappearance of a celestial body behind another or in its shadow.
Phrases and idioms:
immersion heater an electric heater designed for direct immersion in a liquid to be heated, esp. as a fixture in a hot-water tank.
Etymology: ME f. LL immersio (as IMMERSE)