When you break down the word uniqueness, it’s easy to see what it means. First you notice the word unique, which means “one of a kind.” Then you notice -ness, a common suffix that’s used to form nouns that refer to a state of being. Put it together and you get uniqueness, a noun used to describe that certain something that makes a person or thing uncommon or singular, like "the uniqueness of a famous opera singer’s voice."