taru-adjective, adverb taking the 'to' particle
panic-stricken; alarmed; frightened (of the masses)
Rare literary yojijukugo describing a state where people's hearts are agitated and fearful, often used in historical or formal contexts to depict public panic or mass alarm.
戦争の噂に人心恟々として、町は混乱した。
With rumors of war, the people were panic-stricken and the town fell into chaos.
人心恟々たる有様で、誰も冷静ではいられなかった。
In a state of mass alarm, no one could remain calm.
A yojijukugo of Chinese origin, combining 人心 (people's hearts) with 恟々 (fearful, agitated). The exact historical derivation is uncertain, but it follows classical Chinese patterns for describing collective emotional states.