Scandinavian vs Viking

Scandinavian and Viking both are nouns.

Word	Noun	Adjective	Verb	Adverb
Scandinavian	Yes	Yes	No	No
Viking	Yes	No	No	No

As nouns, Viking is a hyponym of Scandinavian; that is, Viking is a word with a more specific, narrower meaning than Scandinavian:

Scandinavian: an inhabitant of Scandinavia
Viking: any of the Scandinavian people who raided the coasts of Europe from the 8th to the 11th centuries

Other hyponyms of Scandinavian include berserk, berserker.

Scandinavian (noun)	Viking (noun)
the northern family of Germanic languages that are spoken in Scandinavia and Iceland	any of the Scandinavian people who raided the coasts of Europe from the 8th to the 11th centuries
an inhabitant of Scandinavia

Scandinavian (adjective)	Viking (adjective)
of or relating to Scandinavia or its peoples or cultures