The base or main part that something is built on.
The house's fundament is its foundation.
这所房子的基础就是它的地基。
The main idea or principle that something is based on.
The fundament of her argument was solid evidence.
她论点的基础是确凿的证据。
The buttocks.
He fell on his fundament.
他摔倒在了他的屁股上。