ascertain

This word carries a strong sense of deliberate verification. It is not a casual discovery, like stumbling upon a fact, but rather a purposeful quest for truth. It implies a process of checking evidence, calculating data, or questioning witnesses to remove all doubt. Because of its precision, the word is primarily used in formal, legal, or technical contexts. You would use it in a police report or a scientific paper, whereas in a casual conversation with friends, you would likely use find out or check.