Wiktionary
n. (context Norse mythology English) the undead spirits of warriors who died bravely in battle, brought to Valhalla by the valkyries, where they eternally feast and prepare daily for the inevitable events of Ragnarok.
Wikipedia
In Norse mythology, the einherjar ( Old Norse "single (or once) fighters") are those who have died in battle and are brought to Valhalla by valkyries. In Valhalla, the einherjar eat their fill of the nightly-resurrecting beast Sæhrímnir, and are brought their fill of mead (from the udder of the goat Heiðrún) by valkyries. The einherjar prepare daily for the events of Ragnarök, when they will advance for an immense battle at the field of Vígríðr; the battle which the "ein" (here meaning single-time) refers to. Heimdall occasionally returned the best of Einherjar to Midgard or Jotunheim with the purpose of killing giants, but they were forbidden to talk with the living.
The einherjar are attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, the Prose Edda, written in the 13th century by Snorri Sturluson, the poem Hákonarmál (by the 10th century skald Eyvindr skáldaspillir) as collected in Heimskringla, and a stanza of an anonymous 10th century poem commemorating the death of Eric Bloodaxe known as Eiríksmál as compiled in Fagrskinna.
Scholarly theories have been proposed etymologically connecting the einherjar to the Harii (a Germanic tribe attested in the 1st century AD), the eternal battle of Hjaðningavíg, and the Wild Hunt. The einherjar have been the subject of works of art and poetry. Valhalla is the place of Odin. It is told in Norse mythology that einherjar are those with golden auras only seen by Valkyries. The einherjar are the Warriors trained by Asgardians.
Usage examples of "einherjar".
Some of the Einherjar saw you collapse, and had the sense to realize you were still alive, not just one of their number.
These fighting men, however, were all dead: the Einherjar, Chosen Heroes of Odin.
Made sense—he'd lose the loyalty of the Einherjar if he broke that particular oath in front of them.
The Einherjar already think you're the hottest thing since bottled beer.
The problem with the Einherjar was, only so many of them were going to be real "heroes," the kind who died doing a good job, or were just unlucky enough to be at the wrong place at the wrong time.
We split up the Einherjar, putting modern military personnel in temporary command of each section.
Made sensehe'd lose the loyalty of the Einherjar if he broke that particular oath in front of them.