Panic, a.
Etymology: [Gr. panique.]
Extreme or sudden and causeless; unreasonable; -- said of fear or fright; as, panic fear, terror, alarm. "A panic fright." Dryden.
2 other Webster entries under this spelling
Panic, n.
(Bot.)
A plant of the genus Panicum; panic grass; also, the edible grain of some species of panic grass. Panic grass (Bot.), any grass of the genus Panicum.
Panic, n.
1. A sudden, overpowering fright; esp., a sudden and groundless fright; terror inspired by a trifling cause or a misapprehension of danger; as, the troops were seized with a panic; they fled in a panic.
2. By extension: A sudden widespread fright or apprehension concerning financial affairs.
Shades of meaning
Fernald has no entry of its own for panic; he lists it under alarm, fear.
Where he writes about it:
Panic is a sudden fear or fright, affecting numbers at once; vast armies or crowded audiences are liable to panic upon slight occasion. — from fear
In a like sense we speak of a financial panic. — from fear