Northman vs berserker

Northman and berserker both are nouns.

Word	Noun	Adjective	Verb	Adverb
Northman	Yes	No	No	No
berserker	Yes	No	No	No

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

Northman: an inhabitant of Scandinavia
berserker: one of the ancient Norse warriors legendary for working themselves into a frenzy before a battle and fighting with reckless savagery and insane fury

Other hyponyms of Northman include Viking, berserk.

Northman (noun)	berserker (noun)
an inhabitant of Scandinavia	one of the ancient Norse warriors legendary for working themselves into a frenzy before a battle and fighting with reckless savagery and insane fury