Source : Webster's Revised Unabridged Dictionary (1913)

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 : WordNet®

immersion
     n 1: sinking until covered completely with water [syn: {submergence},
           {submerging}, {submersion}]
     2: (astronomy) the disappearance of a celestial body prior to
        an eclipse [syn: {ingress}] [ant: {egress}, {egress}]
     3: complete attention; intense mental effort [syn: {concentration},
         {engrossment}, {absorption}]
     4: a form of baptism in which part or all of a person's body is
        submerged
     5: the act of wetting something by submerging it [syn: {submersion},
         {ducking}, {dousing}]