noun
immense sum of money; ten thousand yen
Refers to a very large amount of money, often used in expressions like 万金を費やす (spend a fortune). The literal meaning 'ten thousand yen' is less common in modern usage.
その計画には万金を費やした。
They spent a fortune on that project.
万金を積まれても、その秘密は明かせない。
Even if offered a huge sum of money, I cannot reveal that secret.
大金 is a more common word for a large sum of money, while 万金 has a slightly more literary or emphatic feel.
Compound of 万 (ten thousand, myriad) and 金 (money, gold). The literal meaning 'ten thousand yen' is derived from the components, but the word is primarily used to indicate a vast sum.