Crossword Genius

Less than a pinta! (5)

Ross

I believe the answer is:

cuppa

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'less' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for cuppa that I've seen before include "Refreshing brew" , "Drink of tea (informal)" , "Drink of tea (colloq.)" .)

I've seen this clue in the Evening Standard.
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