Step 1: Understand the concept of a hostile witness.
A witness is ordinarily called by a party to support that party's case. Sometimes, a witness at trial gives testimony that is contrary to the interest of the party that called them.
Step 2: Define the term precisely.
A hostile witness (also called an adverse witness) is one who gives testimony unfavorable to or against the party that called them to the stand. In such a situation, the court may permit the calling party to cross-examine their own witness.
Step 3: Match with options.
Option (4) precisely captures this definition.
\[ \boxed{\text{gives evidence at trial against the party calling him}} \]