Crossword Genius

Bank's raison d'?tre is unique (4)

Ross

I believe the answer is:

rare

I'm a little stuck... Click here to teach me more about this clue!

'is unique' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for rare that I've seen before include "Exceptional" , "Especially good" , "Choice - lightly cooked - thin" , "Infrequent like underdone meat" , "Very infrequent or scarce" .)

I've seen this clue in the Irish Times.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.