unused = not used; fresh; new

1. You can get a refund on the unused tickets.
2. All the unused cheque leaves were surrendered to the bank.
3. Unused car, unused furniture, etc.

disused = no longer being used; abandoned

1. Beware of the disused well near the playground.
2. This bridge was used until the 2000s and then fell into disuse.
3. Long periods of disuse can damage batteries.
4. Disused mine, disused warehouse, etc.

Unused to also means unaccustomed to

1. She was quite unused to this way of life