Capital doubles when interest rate drops (5)

I believe the answer is:

paris

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

'capital' is the definition.
(capital of France)

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

(Other definitions for paris that I've seen before include "foreign city" , "French department" , "He abducted Helen of Troy" , "Prince who abducted Helen, starting a long war (see 8)" , "European capital -- Trojan prince" .)

I've seen this clue in The Guardian.

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.