Passive joiner tweaking cases (5)

I believe the answer is:

inert

'passive' is the definition.
(I've seen this before)

'joiner tweaking cases' is the wordplay.
'cases' indicates the answer is hidden within the clue.
'INERT' is hidden within 'joiner tweaking'.

(Other definitions for inert that I've seen before include "Disinclined to act" , "Unreacting" , "Motionless or lifeless" , "like nitrogen" , "Lifeless; apathetic" .)

I've seen this clue in The Guardian.

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