To prolong something means to make it last longer than it normally would. When a doctor prolongs a patient's life with treatment, she extends it. When you prolong a pleasant conversation by asking another question, you stretch out the enjoyable moment. When a basketball team prolongs the season by making the playoffs, they keep playing instead of ending their year.

You can prolong a visit with your grandparents, prolong a summer vacation by leaving a few days later, or prolong the mystery in a story by holding back clues.

Sometimes prolonging something is good: a coach might prolong practice to give players extra preparation time. Sometimes it's frustrating: a prolonged argument that drags on and on exhausts everyone involved. A prolonged illness lasts much longer than expected.

Notice that prolong suggests deliberate action or effort. Rain doesn't prolong itself, but you might prolong your time outside in the rain by refusing to come in. The word also appears as “prolonged,” meaning extended or drawn out: a prolonged silence, a prolonged drought, or prolonged applause that goes on and on because the audience loved the performance.