Sunbelt vs Sun Belt

Sunbelt and Sun Belt both are nouns.

Word	Noun	Adjective	Verb	Adverb
Sunbelt	Yes	No	No	No
Sun Belt	Yes	No	No	No

As nouns, Sunbelt and Sun Belt are synonyms defined as:

Sunbelt and Sun Belt: states in the south and southwest that have a warm climate and tend to be politically conservative

Sunbelt (noun)	Sun Belt (noun)
states in the south and southwest that have a warm climate and tend to be politically conservative	states in the south and southwest that have a warm climate and tend to be politically conservative