white whale

US /waɪt weɪl/
UK /waɪt weɪl/
"white whale" picture
1.

graal, quête impossible

a goal or object that is extremely difficult to find or achieve

:
Finding a cure for cancer has been the white whale of medical research.
Trouver un remède contre le cancer a été le graal de la recherche médicale.
For many archaeologists, discovering the lost city of Atlantis is their ultimate white whale.
Pour de nombreux archéologues, découvrir la cité perdue de l'Atlantide est leur graal ultime.