Claiming to lose £1,000 over a bloomer (7)

I believe the answer is:

nigella

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

'bloomer' is the definition.
(I know that nigella is a type of bloomer)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for nigella that I've seen before include "TV personality" , "plant" , "Flower and tv cook" , "Love-in-a-mist genus - celebrity cook" , "girl" .)

I've seen this clue in The Guardian.

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