Three cheers for Koichi of Tofugu! Hip hip hooray! Hip hip hooray! Hip hip hooray!
Ten thousand years old! That's a lot of time. This is the word for the turned-English Japanese phrase, banzai!
The reading isn't the same as 万's normal reading. It's ばん instead of まん. But, since the word "banzai" is so well known, you probably can remember this reading.