Viet Nam vs Vietnam

Viet Nam and Vietnam both are nouns.

Word	Noun	Adjective	Verb	Adverb
Viet Nam	Yes	No	No	No
Vietnam	Yes	No	No	No

As nouns, Viet Nam and Vietnam are synonyms defined as:

Viet Nam and Vietnam: a communist state in Indochina on the South China Sea; achieved independence from France in 1945

Other synonyms of Viet Nam include Annam, Socialist Republic of Vietnam.

Viet Nam (noun)	Vietnam (noun)
a communist state in Indochina on the South China Sea; achieved independence from France in 1945	a prolonged war (1954-1975) between the communist armies of North Vietnam who were supported by the Chinese and the armies of South Vietnam who were supported by the United States
	a communist state in Indochina on the South China Sea; achieved independence from France in 1945