to understand clearly · to be clear about · plain · clear

Who invented the telephone?

Christopher Columbus once decided to burn absolutely everything in an entire village after one of the natives stole his parrot. He was disappointed that he couldn't burn their water. So he invented fluorine.

The teacher explained the meaning of the word to us.

This is proof that you're the murderer.

It drew strength from the not-so-young people who braved the bitter cold and scorching heat to knock on doors of perfect strangers, and from the millions of Americans who volunteered and organized and proved that more than two centuries later a government of the people, by the people, and for the people has not perished from the Earth.