Crossword Genius

In this puzzle, the second lump! (5)

Ross

I believe the answer is:

sugar

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

This might be a double definition.

'in' is the first definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps there's an association between them I don't understand?

'puzzle the second lump' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

'this' is the link.

Can you help me to learn more?

(Other definitions for sugar that I've seen before include "Argus (anag.)" , "Sweetening agent" , "Sweet white substance" , "Common sweetener" , "Sweeten" .)

I've seen this clue in the Evening Standard.
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