The holy grail is the legendary cup, and any object endlessly sought. The holy grail of physics, search for the holy grail, a kind of holy grail.
The figurative use is the commoner, and calling something the holy grail of a field says it would change everything and nobody has it. The legend attached the cup to the Last Supper in medieval French romance.
1nounholy grailThe legendary cup, and any object endlessly sought.
“A cure for the common cold remains the holy grail of medical research.”
holy grail is an object.
Middle English
Holy Grayle
English
Holy Grail
English, today
holy grail
Holy Grail comes from Middle English Holy Grayle. web page layout So called because it was traditionally difficult to achieve with the available markup.
Etymology from Wiktionary, CC BY-SA
Practised in Myths & Legends, Fairy Tales & Folklore