In this way sleuth uses envelopes (4)

I believe the answer is:

thus

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'in this way' is the definition.
(synonyms)

'sleuth uses envelopes' is the wordplay.
'THUS' is hidden within the letters.
However, I'm uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for thus that I've seen before include "Shut (anag.)" , "an original Christmas gift" , "Like so" , "In this manner" , "as indicated" .)

I've seen this clue in The Times.

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