Crossword Genius

Something productive in retirement? (9)

Ross

I believe the answer is:

soporific

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

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for soporific that I've seen before include "Sedative" , "making one nod" , "Causing sleepiness" , "Inducing mental lethargy" , "Inducing drowsiness or sleep" .)

I've seen this clue in The Guardian.
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