solitarykey
nounUK /ˈsɒlɪtəri kiː/
US /ˈsɑːləteri kiː/
A single key that is all alone and has no other keys with it.
She found a solitarykey lying on the empty table.
OTHER MEANINGS
2. A key that works by itself without needing any other key.
The old chest opened with a solitarykey.
3. A quiet, lonely key that is kept apart from the rest.
He kept the solitarykey in a small box by itself.
4. A special key used alone to unlock something important.
Only the solitarykey could open the garden gate.