Busan vs Pusan

Busan and Pusan both are nouns.

Word	Noun	Adjective	Verb	Adverb
Busan	Yes	No	No	No
Pusan	Yes	No	No	No

As nouns, Busan and Pusan are synonyms defined as:

Busan and Pusan: a city in southeastern South Korea on the Korean Strait; the chief port and second largest city

Busan (noun)	Pusan (noun)
a city in southeastern South Korea on the Korean Strait; the chief port and second largest city	a city in southeastern South Korea on the Korean Strait; the chief port and second largest city