Crossword Genius

Secret service technique (9)

Ross

I believe the answer is:

underhand

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'secret' is the definition.
(underhand means secret or duplicitous)

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for underhand that I've seen before include "servant of lower rank" , "Unsporting" , "way of delivering service." , "In a secret or dishonest way" , "Deceitful" .)

I've seen this clue in The Sunday Times and The Times.
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