longship vs ship

longship and ship both are nouns.

Word	Noun	Adjective	Verb	Adverb
longship	Yes	No	No	No
ship	Yes	No	Yes	No

As nouns, ship is a hypernym of longship; that is, ship is a word with a broader meaning than longship:

longship: a type of ship invented and used by the Vikings for trade, commerce, exploration, and warfare during the Viking Age.
ship: a vessel that carries passengers or freight

longship (noun)	ship (noun)
a type of ship invented and used by the Vikings for trade, commerce, exploration, and warfare during the Viking Age.	a vessel that carries passengers or freight