1) Curiosity 2) One in a million 3) Oner 4) Singular find 5) Uncommon creature 6) Uncommon sort 7) Uncommon thing 8) Unusual one 
Rara avis is Latin for A rare bird
rara avis Rare bird. An unusual or exceptional person or thing; someone out of the ordinary. It was first used figuratively by the Roman satirist Juvenal. Rara avis in terris nigroque simillima cycno. 'A bird rarely seen on earth, and very like a black swan.' Juvenal chose a black swan for his comparison because the Romans had no idea that black...