Essential ingredients to cook rabbit gumbo (4)

I believe the answer is:

okra

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

'gumbo' is the definition.
(synonyms)

'essential ingredients to cook rabbit' is the wordplay.
'OKRA' is hidden within the letters.
But, I'm unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for okra that I've seen before include "Green pods, in stews" , "Tropical plant with edible pods" , "Bhindi or lady's finger" , "Edible seed pods" , "old ladies' fingers" .)

I've seen this clue in The Independent.

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