Crossword Genius

The placebo the doctor gave the hypochondriac? (5,5)

Ross

I believe the answer is:

tonic water

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'the placebo' 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 tonic water that I've seen before include "something for your gin?" , "Accompaniment to gin" , "Aerated quinine drink" , "Mixer" , "Non-alcoholic drink" .)

I've seen this clue in the Evening Standard.
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