Crossword Genius

Geraldine corners marketplace (4)

Ross

I believe the answer is:

aldi

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

'corners marketplace' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'geraldine' is the wordplay.
'ALDI' is hidden in amongst the letters.
However, I am unsure how this is indicated.

Can you help me to learn more?

(Another definition for aldi that I've seen is " German-based supermarket chain".)

I've seen this clue in the Sydney Morning Herald.
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