From Old Norse eiskra (“rage before hot excitement”), from Proto-Germanic *aiskrōną (“to rage”), according to Pokorny, from Proto-Indo-European *aisk- (“shining, bright”), comparable to Proto-Slavic *jьskra (“spark”). However, compare *h₂ey- (“to energize, to invigorate”) and *h₂eydʰ- (“to ignite”). Possibly related to Ancient Greek ἐσχάρᾱ (eskhárā, “hearth”).