determine
To figure something out or decide it for sure.
To determine means to figure something out, decide it, or make it happen through your choices and actions.
When scientists determine the age of a fossil, they use careful measurements and tests to figure out how old it is. When a judge determines the winner of a science fair, she examines all the projects and decides which one deserves first place. When you determine the answer to a challenging math problem, you work through the steps until you discover the solution.
The word carries a sense of purpose and finality. You don't just guess or wonder: you actively work to reach a solid conclusion or make a firm decision. A detective determines who committed a crime by gathering evidence and eliminating possibilities until the truth becomes clear.
You might also hear people say someone is determined, which describes a person who has decided on a goal and won't give up until they reach it. A determined athlete keeps practicing even when progress feels slow.
The word appears often in serious contexts because determining something matters. Whether you're determining the cause of a problem, the best solution, or your own path forward, you're taking responsibility for reaching a real answer.