Ratified December 15, 1791
A safeguard against a specific worry the framers had: that listing certain rights (in the other nine amendments) might be read to imply that any right not listed doesn't exist. This amendment says the opposite — the list isn't exhaustive, and the people retain other rights beyond what's written down.
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.