wildcat

Concise Oxford English Dictionary © 2008 Oxford University Press:
wildcat/ˈwʌɪldkat/

▶noun

• 1 a small Eurasian and African cat, typically grey with black markings and a bushy tail, believed to be the ancestor of the domestic cat. [Felis silvestris.]

  ■ a bobcat or other small felid.

• 2 a hot-tempered or ferocious person.

• 3 an exploratory oil well.

▶adjective

• 1 (of a strike) sudden and unofficial.

• 2 commercially unsound or risky.

▶verb US prospect for oil.

– derivatives
wildcatter noun.