Singapore vs Singapore Island

Singapore and Singapore Island both are nouns.

Word	Noun	Adjective	Verb	Adverb
Singapore	Yes	No	No	No
Singapore Island	Yes	No	No	No

As nouns, Singapore and Singapore Island are synonyms defined as:

Singapore and Singapore Island: an island to the south of the Malay Peninsula

Singapore (noun)	Singapore Island (noun)
a country in southeastern Asia on the island of Singapore; achieved independence from Malaysia in 1965	an island to the south of the Malay Peninsula
an island to the south of the Malay Peninsula
the capital of Singapore; one of the world's biggest ports