What does the prefix e mean in word emit?

The prefix "e-" in the word "emit" doesn't have a clear, independent meaning like some prefixes do (like "pre-" meaning before or "un-" meaning not).

Instead, "e-" in "emit" is part of a root word "mittere" which is Latin for "to send." The "e-" is used to create a verb from the root word.

So, "emit" literally means "to send out" or "to give off".