Pusan vs Busan

Pusan and Busan both are nouns.

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

As nouns, Pusan and Busan are synonyms defined as:

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

Pusan (noun)	Busan (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