Marco wrote,

> Hello!
>
> The ending can be applied also to common nouns, so
> /Víkingar/ derived their name from /vík/ "bay". The original
> meaning was "pirates".
>

At least we agree that "Vik" was not the family ancestor.
I can just as readily see -ing as a suffix that is applied
to adjectives, in order to make them into nouns.

example: fagr - fegringr,
svartr - svertingr.

or to verbs:

klofna - klofningr.

víkingr m. is probably derived from víking f.
The first noun describing a type of person,
the second one a kind of activity.

The root vík may be related to the verb víkja, that
describes a kind of motion. For example, in modern Danish,
they have the word "afvik" which signifies a "deviation".

Best,
Xigung.