Why was "tantrum" trending last week?
Scandinavian pirate, 1807, vikingr; modern spelling attested from 1840. The word is a historical revival; it was not used in Middle English, but it was revived from Old Norse vikingr "freebooter, sea-rover, pirate, viking," which usually is explained as meaning properly "one who came from the fjords," from vik "creek, inlet, small bay" (cf. Old English wic, Middle High German wich "bay," and second element in Reykjavik). But Old English wicing and Old Frisian wizing are almost 300 years older, and probably derive from wic "village, camp" (temporary camps were a feature of the Viking raids), related to Latin vicus "village, habitation" (see villa).
The connection between the Norse and Old English words is still much debated. The period of Viking activity was roughly 8c. to 11c. In the Anglo-Saxon Chronicle, the raiding armies generally were referred to as þa Deniscan "the Danes," while those who settled in England were identified by their place of settlement. Old Norse viking (n.) meant "freebooting voyage, piracy;" one would "go on a viking."