Sticky extract of legumes (3)

I believe the answer is:

gum

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'sticky extract' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'of legumes' is the wordplay.
'of' indicates a hidden word.
'GUM' is hidden within 'legumes'.

Can you help me to learn more?

(Other definitions for gum that I've seen before include "Glue; jelly-like sweet" , "Gingeva is its technical name" , "Sticky plant substance" , "Sticky substance and mouth tissue" , "Part of mouth; a tree" .)

I've seen this clue in the Evening Standard.

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