to be the only one of a particular type of thing or person.
As a female engineer who began her career in the 1940s, she was one of a kind.
be one of a kind
To have no equal; to be very unique. This opportunity is one of a kind—you have to take it!This design is one of a kind, as the artist only ever made one.Not many people have so much talent at such a young age. This kid is truly one of a kind.