Immersion \Im*mer"sion\, n. [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.

Source: Webster's Revised Unabridged Dictionary (1913)