noun which may take the genitive case particle 'no'
unused; not yet used
Describes something that has not been used, often in a brand-new or pristine state. Commonly used for items, tickets, or resources.
I collect unused stamps.
There is an unused notebook in the drawer.
This card is unused.
I ended up leaving the ticket unused.
If you sell it unused, it fetches a higher price.
未使用 just means something has never been used, while 遊休 implies a resource that could be used but is currently sitting idle.
未開封 means 'unopened' (the packaging hasn't been broken), whereas 未使用 means 'unused' and can apply even to opened items that were never actually used.
unused item; never-used item
older woman who has never had children
Compound of 未 (mi, 'not yet') and 使用 (shiyō, 'use').