immersionn.[L. immersio; cf. F. immersion.]1. The act of immersing, or the state of being immersed; a sinking within a fluid; a dipping; as, the immersion of Achilles in the Styx.()2. Submersion in water for the purpose of Christian baptism, as, practiced by the Baptists.()3. The state of being overhelmed or deeply absorbed; deep engagedness.()Too deep an immersion in the affairs of life. (Atterbury.)4. (Astron.) The dissapearance of a celestail body, by passing either behind another, as in the occultation of a star, or into its shadow, as in the eclipse of a satellite; -- opposed to emersion.()Immersion lens, a microscopic objective of short focal distance designed to work with a drop of liquid, as oil, between the front lens and the slide, so that this lens is practically immersed.()