As

As is used to compare things, show the reason for something, or say that two things happen at the same time, as in “as tall as,” “as it was raining,” or “as he walked.” It can also mean “in the role of,” as in “work as a teacher.”

From Old English “alswa” or “also” meaning “in like manner,” which was shortened over time. The word gradually took on several related uses for comparison and time.