incomparable, uncomparable

The prefix ‑in in incomparable serves as an intensive. Thus, incomparable means “so good as to be beyond comparison.” The -un in uncomparable serves as a negative. Thus, uncomparable means “not subject to comparison.”

When you pronounce either word, the accent falls on -com, not -par.

Example: The actress’s incomparable performance in the movie prompted critics to note that her previous performances were simply uncomparable.