User blog comment:Lancebruh/Question about Tenjin and Bishamonten/@comment-5291630-20150423233728

“Vaisravana” is the original name of the Buddhist god in Sanskrit. However, because Chinese can’t 100% faithfully represent Sanskrit readings with Chinese letters, it was approximated with 毘沙門天 (Pishamen-tian). When the word was then adopted into Japanese, it also adopted the Japanese readings of the characters, which come out as "Bishamon-ten". The “ten” suffix is just a way of denoting that it’s the name of a god, so it’s sometimes there or sometimes not. The same way Yato is sometimes called "Yato-gami".

It's pretty much the exact same thing that led to the whole "God", "Yaweh", "Jehovah", and "Allah" thing in Western religions. You have a term that went from Hebrew to Greek to English and Arabic, and while they all refer to the same thing, because of getting filtered through multiple languages we ended up with multiple terms.

Tenjin is a god who was once human. His human name was Sugawara no Michizane, and after he died, there were a lot of natural disasters that people blamed on his vengeful spirit, so the people decided to revere him as a god to placate him, and gave him the posthumous name Tenma Tenjin, or just Tenjin.

"Binbou-gami" is technically Kofuku's real name, she just took on the name "Ebisu Kofuku" for the public because "god of poverty" sounded bad.