Silence on crux of industrial disease (9)
I believe the answer is:
stillness
'silence on crux of industrial disease' is the definition.
'stillness' can be an answer for 'silence' (stillness is a kind of silence). I am unsure of the 'on crux of industrial disease' bit.
'silence on crux of industrial disease' is the wordplay.
'silence' becomes 'still' (still is a kind of silence).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'crux of industrial disease' becomes 'ness' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'still'+'ness'='STILLNESS'
Can you help me to learn more?
(Other definitions for stillness that I've seen before include "Tranquil silence, calmness" , "Motionlessness" , "Tranquillity, calm" , "Quiet, calm" , "Lack of activity" .)