Siam vs Kingdom of Thailand

Siam and Kingdom of Thailand both are nouns.

Word	Noun	Adjective	Verb	Adverb
Siam	Yes	No	No	No
Kingdom of Thailand	Yes	No	No	No

As nouns, Siam and Kingdom of Thailand are synonyms defined as:

Siam and Kingdom of Thailand: a country of southeastern Asia that extends southward along the Isthmus of Kra to the Malay Peninsula

Other synonyms of Siam include Thailand.

Siam (noun)	Kingdom of Thailand (noun)
a country of southeastern Asia that extends southward along the Isthmus of Kra to the Malay Peninsula	a country of southeastern Asia that extends southward along the Isthmus of Kra to the Malay Peninsula