No money for more bananas, one calculates (5)

I believe the answer is:

adder

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

'no' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for adder that I've seen before include "Mathematical reptile" , "British snake; summer" , "calculator?" , "Venomous type" , "One creature" .)

I've seen this clue in The Independent.

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