As (conjunction)

1. Used to indicate similarity or equality.
2. In the capacity, character, or role of.
3. While considering or in accordance with the fact that.

Origin:

Old english, from proto-germanic *alsi, probably originally meaning “through which”, from proto-indo-european *h₂el- 'beyond, other' and *-si, a suffix denoting instrumental case.

Examples:

1. I work as a teacher.
2. He sang as loudly as he could.
3. As a child, she loved to play outside.
4. As we discussed yesterday, the project deadline is approaching quickly.
5. As you know, our company policy is to provide excellent customer service.