*wild-cat*

a. 1. Unsound; worthless; irresponsible; unsafe; -- said to have been originally applied to the notes of an insolvent bank in Michigan upon which there was the figure of a panther. [ 1913 Webster ]

2. (Railroad) Running without control; running along the line without a train; as, a wild-cat locomotive. [ 1913 Webster ]

[ 1913 Webster ]