Oh! We also have a rogue key...
rogue
noun:
1. An unprincipled, deceitful, and unreliable person; a scoundrel or rascal.
2. One who is playfully mischievous; a scamp.
3. A wandering beggar; a vagrant.
4. A vicious and solitary animal, especially an elephant that has separated itself from its herd.
5. An organism, especially a plant, that shows an undesirable variation from a standard.
adj.:
1. Vicious and solitary. Used of an animal, especially an elephant.
2. Large, destructive, and anomalous or unpredictable: a rogue wave; a rogue tornado.
3. Operating outside normal or desirable controls: "How could a single rogue trader bring down an otherwise profitable and well-regarded institution?"