Roundhead vs friend

Roundhead and friend both are nouns.

Word	Noun	Adjective	Verb	Adverb
Roundhead	Yes	No	No	No
friend	Yes	No	No	No

As nouns, friend is a hypernym of Roundhead; that is, friend is a word with a broader meaning than Roundhead:

Roundhead: a supporter of parliament and Oliver Cromwell during the English Civil War
friend: a person who backs a politician or a team etc.

Other hypernyms of Roundhead include admirer, booster, champion, protagonist, supporter.

Roundhead (noun)	friend (noun)
a supporter of parliament and Oliver Cromwell during the English Civil War	a person you know well and regard with affection and trust
	a person with whom you are acquainted
	an associate who provides cooperation or assistance
	a person who backs a politician or a team etc.