Register means to officially record or sign up for something. When you register for a class, you put your name on the official list of students taking it. When your parents register to vote, they add their names to the list of people allowed to vote in elections. Libraries keep a register of everyone who has a library card.

Register also means to show or express something, especially a feeling or reaction. If shock registers on someone's face, you can see their surprise clearly. A thermometer registers temperature. When you register a complaint, you officially make your objection known.

As a noun, a register can be an official list or record, like a class register or a library register.

In another sense, register refers to a level or style of language. You might use a formal register when writing a letter to the principal, using complete sentences and polite phrases. With friends, you'd use a casual register with slang and relaxed grammar. Learning which register fits each situation helps you communicate effectively, whether you're texting a friend, giving a presentation, or writing a thank-you note to your grandmother.