He and Ottar used to go viking together
This is a cool reanalysis of the noun viking as a verb "to vike" with the -ing suffix. One possible etymology of Old Norse víkingr is that it is a combination of vík "creek, inlet" plus the suffix -ingr, which I assume is cognate with English -ing.
A second derivation is suggested by the Oxford Dictionary of English Etymology: the Old Norse word is dated from the 10th century, but the existence of Old English wīcingsċeaþa "piraticus"¹ in the 8th century, and Old Frisian wītsing, wīsing, suggests that víkingr was borrowed from Old English wīc or Old Frisian wīk in the sense of "camp": "the formation of temporary encampments being a prominent feature of viking raids." If this is true, it means that viking is derived from *weiḱ- and related to ecology and villain.
Uig, a town on the Isle of Skye, where I once spent a few days, is derived from Old Norse vík. Or so I was told.
Acephalous reports that the OED has a strange and outdated definition of viking: "One of those Scandinavian adventurers who practised piracy at sea and committed depredations on land."
1. I assume that "piraticus" refers to piracy and not spiders.