Siam vs Thai

Siam and Thai both are nouns.

Word	Noun	Adjective	Verb	Adverb
Siam	Yes	No	No	No
Thai	Yes	Yes	No	No

Siam (noun)	Thai (noun)
a country of southeastern Asia that extends southward along the Isthmus of Kra to the Malay Peninsula	a branch of the Tai languages, spoken in central Thailand, centered in Bangkok
	a native or inhabitant of Thailand

Siam (adjective)	Thai (adjective)
	of or relating to Thailand
	of or relating to the languages of the Thai people
	of or relating to or characteristic of Thailand or its people