Helsingfors vs Helsinki

Helsingfors and Helsinki both are nouns.

Word	Noun	Adjective	Verb	Adverb
Helsingfors	Yes	No	No	No
Helsinki	Yes	No	No	No

As nouns, Helsingfors and Helsinki are synonyms defined as:

Helsingfors and Helsinki: the capital and largest city of Finland; located in southern Finland; a major port and commercial and cultural center

Other synonyms of Helsingfors include capital of Finland, Finnish capital.

Helsingfors (noun)	Helsinki (noun)
the capital and largest city of Finland; located in southern Finland; a major port and commercial and cultural center	the capital and largest city of Finland; located in southern Finland; a major port and commercial and cultural center