The Collaborative International Dictionary of English v.0.48:

Wild-cat \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]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "wildcat":
   Jezebel, Leo, Siberian tiger, adventurous, aleatory, beldam,
   bitch-kitty, bobcat, cat-a-mountain, catamount, chancy, cheetah,
   cougar, dicey, disobedient, full of risk, fury, grimalkin, hag,
   hazardous, headstrong, heady, hellcat, hellhag, insubordinate,
   irresponsible, jaguar, lawless, leopard, licentious, lion, lynx,
   mountain lion, mutinous, ocelot, painter, panther, puma, rampant,
   reinless, riskful, risky, self-willed, she-devil, she-wolf, simba,
   siren, speculative, termagant, tiger, tigress, unaccountable,
   unbridled, unchecked, uncontrolled, uncurbed, undisciplined,
   ungoverned, unreined, unrestrained, venturesome, venturous, virago,
   vixen, willful, witch