rara avis

ra·​ra avis | \ ˌrer-ə-ˈā-vəs , ˌrär-ə-ˈä-wəs \

plural rara avises\ ˌrer-​ə-​ˈā-​və-​səz \ or rarae aves\ ˌrär-​ˌī-​ˈä-​ˌwās \

Definition of rara avis

: someone or something that is rare : RARITY sense 2

Elizabeth Bishop was the anomaly, the rara avis, of her generation of poets …— Harper's

It is easy to see why Ms. Hacker's early work had such an impact; a rara avis in the swamp of free verse, she writes villanelles, sestinas and sonnets …— David Kirby

And she has become that rara avis, a serious medievalist with a popular following.— Patrick J. Geary

The Bob Dorough-Dave Frishberg concert at Kaye Playhouse on June 19 is sure to sell out, combining two comparable rarae aves—clever, storytelling jazz songwriters.— Ben Ratliff

Source: Merriam-Webster