N-SING
義務；責任;職責
If you say that the onus is on someone to do something, you mean it is their duty or responsibility to do it.
例句
The onus is on the shopkeeper to provide goods which live up to the quality of their description...
店主有義務提供質量與其描述相符的商品。
The onus of proof is reversed in libel actions and placed firmly on the defender.
在誹謗訴訟中，舉證責任反過來由辯方全權承擔。