A more thorough explanation:

An adverse witness, also known as a hostile witness, is someone who supports the opposing party in a legal case because they have a relationship or common interest with them. For instance, if the state is prosecuting a defendant in a criminal case, a witness who supports the state's position is an adverse witness to the defendant. However, if the witness is not a party to the case and has no legal interest in the outcome, they are not an adverse witness.

It is crucial to have the right to cross-examine and potentially discredit an adverse witness to ensure a fair trial and due process. Additionally, a party can ask leading questions when interrogating an adverse witness.

In a divorce case, the wife's sister testifies against her brother-in-law, who is the husband. The sister is an adverse witness to the husband because she supports her sister's position. The husband's lawyer can cross-examine the sister to challenge her testimony and credibility.