The prefix re- means to do something again or to do something back. When you rewrite a paragraph, you write it again. When you retell a story, you tell it again. When you replay a video game level, you play it again.

Sometimes re- means to restore something to how it was before. When you refill a water bottle, you fill it back up. When you repay money you borrowed, you pay it back. When you rebuild a sandcastle after a wave destroys it, you build it back to its original form.

The prefix re- attaches to thousands of English words. You can reread a confusing sentence, rethink a bad decision, or redecorate your bedroom. Scientists might retest an experiment to check their results. A director might refilm a movie scene that didn't turn out right.

Not every word starting with r-e uses this prefix, though. Words like red, reason, and receive aren't about doing something again; the r-e just happens to be there as part of the original word. But when you spot re- at the beginning of an action word (a verb), it usually signals repetition or restoration.