Immersion/ɪˈmɜːrʒn/ Definition 1 of 3Pro Tip 1/2Physical Action Remember, immersion involves physically putting things into liquids. The immersion of the jewelry in the cleaning solution made it shine. Pro Tip 2/2Complete Coverage Immersion means the whole item must be underwater, not just part. When testing waterproof watches, they require complete immersion in a tank.