Gulf of Thailand vs Gulf of Siam

Gulf of Thailand and Gulf of Siam both are nouns.

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

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

Gulf of Thailand and Gulf of Siam: an arm of the South China Sea between Indochina and the Malay Peninsula

Gulf of Thailand (noun)	Gulf of Siam (noun)
an arm of the South China Sea between Indochina and the Malay Peninsula	an arm of the South China Sea between Indochina and the Malay Peninsula