Toughness on island in sound? Just the opposite (10)
I believe the answer is:
resilience
'toughness' is the definition.
'on island in sound? just the opposite' is the wordplay.
I cannot really see how this works, but
'on' could be 're' (regarding) and 're' is found in the answer.
'island' could be 'i' (geographical abbreviation) and 'i' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for resilience that I've seen before include "make quick recovery" , "this makes for a speedy recovery" , "Ability to bounce back" , "Ability to spring back" , "Ability to recover fast" .)