Sui generis is a formal adjective used to describe someone or something in a class or group of its own, or in other words, unlike anyone or anything else.

// As a scholar, she is sui generis, head and shoulders above everyone else in her field.

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“TV on the Radio, the celebrated group whose experimental amalgam of rock, post-punk, electronic, and soul made it sui generis in the 2000s New York scene, knew it was time for a break. It was 2019, and after nearly 20 years and five albums together, the nonstop demands of recording and touring had taken its creative and physical toll.” — Jason Newman, Rolling Stone, 16 Apr. 2025

Many English words ultimately trace back to the Latin forms gener- or genus (which are variously translated as “birth,” “race,” “kind,” and “class”). Offspring of those roots include general, generate, generous, generic, and gender. But sui generis is truly a one-of-a-kind genus descendant that English speakers have used to describe singular things since the late 1600s. Its earliest uses were in scientific contexts, but where it once mostly characterized substances, principles, diseases, and even rocks thought to be the only representative of their class or group, its use expanded by the early 1900s, and it is now used more generally for anything that stands alone.