I’m wondering why this particular form of the word is being used rather than ‘vikings’. What’s with the r? The reason I’m wondering is because in all three Scandinavian languages (Danish, Norwegian, Swedish) we use r to denote plural. So in (modern) Danish, we’d have ‘en viking (one viking), flere vikinger (several vikings). Vikingrs to my ear sounds like some sort of double plural form. Like catses and dogses instead of cats and dogs. Admittedly I’m not strong in any sort of etymology in any language, so I don’t know if this is some sort of Old English thing, it just sounds a bit odd to me.