The exact translation of Miruvor or Miruvóre, is not known, but “death-defeater” is a probable etymological meaning. It’s certainly an accurate description.
Appearing in The Fellowship of the Rings, miruvor is a warm and fragrant clear cordial made by and consumed by the Elves. They do not reveal how miruvor was made, but it is thought to come from the honey of the undying flowers in the gardens of Yavanna in Valinor. It’s possible that this drink holds the secret of Elven immortality, although if so, it has no such effect on humans, hobbits or dwarves.
The cordial gives the drinker renewed strength and vitality, and is used by the Elves at their festivals. Some party animals, those Elves, huh?