Which of the following words is synonymous with unprecedented?

The word "unprecedented" refers to something that has never happened before or is unlike anything that has come before it. It conveys a sense of novelty or uniqueness. The choice "unusual" aligns well with this meaning, as it describes something that deviates from what is normal or expected, suggesting it is out of the ordinary.

In contrast, the other options do not fit the meaning of "unprecedented." "Common" and "ordinary" both imply a frequency or regularity that is opposite to the idea of something being unprecedented. "Memorable" relates to something worth remembering, which does not directly connect to the sense of being without prior example. Therefore, "unusual" is the most appropriate synonym for "unprecedented," as both suggest a departure from the norm.