Zuider Zee vs Zuiderzee

Zuider Zee and Zuiderzee both are nouns.

Word	Noun	Adjective	Verb	Adverb
Zuider Zee	Yes	No	No	No
Zuiderzee	Yes	No	No	No

As nouns, Zuider Zee and Zuiderzee are synonyms defined as:

Zuider Zee and Zuiderzee: a former inlet of the North Sea in the northern coast of the Netherlands; sealed off from the sea in 1932 by a dam that created the IJsselmeer

Zuider Zee (noun)	Zuiderzee (noun)
a former inlet of the North Sea in the northern coast of the Netherlands; sealed off from the sea in 1932 by a dam that created the IJsselmeer	a former inlet of the North Sea in the northern coast of the Netherlands; sealed off from the sea in 1932 by a dam that created the IJsselmeer