(uncountable) Overwhelming fear or fright, often affecting groups of people or animals; an instance of this; a fright, a scare.

(countable, computing) Short for kernel panic (“on Unix-derived operating systems: an action taken by the operating system when it cannot recover from a fatal error”); any computer system crash.

(countable, economics, finance) A rapid reduction in asset prices due to broad efforts to raise cash in anticipation of such prices continuing to decline.

(countable, US, originally theater, colloquial) A highly amusing or entertaining performer, performance, or show; a riot, a scream.

(originally) Foxtail millet or Italian millet (Setaria italica), the second-most widely grown species of millet.

(by extension) A plant of the genus Panicum, or of similar plants of other genera (especially Echinochloa and Setaria) formerly included within Panicum; panicgrass or panic grass.

The edible grain obtained from one of the above plants.

(transitive) Cause someone to feel overwhelming fear or fright, to frighten someone into acting hastily, to cause a computer system to crash, or to highly amuse, entertain, or impress an audience watching a performance or show.

(intransitive) To feel overwhelming fear or fright, to lose one's head, or for a computer system to crash.

(by extension (see the etymology)) An adjective "panic" describes something that is characterized by overwhelming or sudden fear or fright.