To make up something means to invent or create it, especially a story, excuse, or explanation that isn't true. When a student makes up a reason for missing homework, they're creating a fictional explanation instead of telling the truth. Writers make up characters and plots for their stories, which is perfectly fine because everyone knows fiction is invented.

The phrase can also mean to reconcile or become friends again after an argument. When two friends make up after a disagreement, they forgive each other and restore their friendship. You might hear someone say “let's make up” when they're ready to stop being angry and move forward.

Makeup (written as one word) refers to cosmetics like lipstick, powder, or eye shadow that people apply to their faces. Stage actors wear heavy makeup so the audience can see their features clearly from far away.

When you make up for something, you compensate for a mistake or loss. If you miss your sister's recital, you might make up for it by taking her out for ice cream and apologizing sincerely. A student who does poorly on one test can sometimes make up for it by studying harder and doing well on the next one.

Finally, things that make up a whole are the parts that compose or form it. The fifty states make up the United States. Atoms make up molecules, which make up everything around us.