one-off

Occurring once, independent of any pattern; one-time.

The government insisted that the embarrassing loss of the tax records was a one-off event.

Seeing Halley's Comet is a one-off, once-in-a-lifetime opportunity.

Special; remarkable; rare; unusual.

BMW is to create a one-off tribute to the iconic 3.0 CSL.

Grammy award-winning singer Celine Dion will reportedly earn $2 million for a one-off performance at the 2024 Olympics.

Something that is done, created, etc. only once, and often quickly, simply, or improvisationally.

Near-synonym: stand-alone

I'll put together a quick one-off as a sample so we can taste the recipe.

Something unique and remarkable.

Near-synonym: stand-alone

It is a one-off; there is nothing else like it.