Here's a breakdown of the etymology:
* Pro-: A prefix meaning "forward" or "out."
* Trahere: The Latin verb meaning "to draw" or "to pull."
Therefore, a protractor is a tool that helps you "draw forth" or "extend" lines and angles.
It's interesting to note that the word "protractor" was first used in the early 1700s, around the same time that the tool itself became popularized. This suggests that the name was likely chosen because it accurately describes the tool's function.