Does co-worker mean the same as colleague?
No. A coworker usually means someone who works at the same
place. Colleague is usually use to refer to someone who works in
the same field (at least approximately).
So, if you're a professor at Harvard University, the janitor at
Harvard is a "coworker", but he's probably not a colleague. A
professor at Stanford University, on the other hand, is a
colleague, but not really a coworker.