Gulf of Siam vs Gulf of Thailand

Gulf of Siam and Gulf of Thailand both are nouns.

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

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

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

Gulf of Siam (noun)	Gulf of Thailand (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