Here's a breakdown of its evolution:
* "Make up" originally meant "to create or invent something."
* Over time, it also came to mean "to apply cosmetics to the face," as in, "to make up one's face."
* Eventually, the phrase was shortened to "makeup", becoming the standard term for cosmetics.
So, "makeup" is called "makeup" because it's a shortened form of the phrase "to make up one's face," which refers to the act of applying cosmetics.