One-off and Rara avis

One-off noun - A happening that occurs only once and is not repeated.

Rara avis and one-off are semantically related In some cases you can replace phrase "Rara avis" with "One-off", this phrases are similar.

Rara avis noun - A rare or unique person.

One-off and rara avis are semantically related (British) in oddity topic. Sometimes you can use "One-off" instead a noun phrase "Rara avis". informal substitute