Or... Maybe both the word viking and vik as in Viken comes from the same verb vikja that means to move (away). The idea being that a vik is where the costline moves away from the "sea road", the "NorWay" ;)

By the way, another word used for Viken (when used for the Oslofjord) is Folden, which means "the fold", so it is where the costline moves or folds away. Also, the counties on the west and east side of Oslofjord was until resently Vestfold and Østfold (meaning west and east (of the) fold)