Thyself is an old-fashioned way of saying “yourself.” You might recognize it from the famous line “To thine own self be true,” which means to be honest with yourself and stay true to your values.

The word appears in Shakespeare's plays, the King James Bible, and other writings from hundreds of years ago. Back then, English speakers used thee, thou, and thy the way we now use you and your. So thyself was the everyday word for “yourself.”

Today, people only use thyself when they're quoting old texts, writing poetry, or trying to sound formal or archaic. You might see it in historical fiction or hear it in a play set in medieval times. A knight might say, “Prepare thyself for battle!” where we would simply say, “Prepare yourself for battle!”

The word reminds us that language changes over time. Words that were normal and common in Shakespeare's era now sound fancy or strange to our ears. When you encounter thyself in a book or play, it's a signal that you're reading something written long ago or something deliberately imitating that older style of speech.