Definitions of wildcat:

• noun:   any small or medium-sized cat resembling the domestic cat and living in the wild
• noun:   an exploratory oil well drilled in land not known to be an oil field
• noun:   a cruelly rapacious person
• adjective:   outside the bounds of legitimate or ethical business practices

  Example: "Wildcat currency issued by irresponsible banks"

• adjective:   (of a mine or oil well) drilled speculatively in an area not known to be productive

  Example: "Drilling there would be strictly a wildcat operation"

• adjective:   without official authorization

  Example: "Wildcat work stoppage"