This is the 8463rd most frequent Japanese word.
戦く
To tremble or shudder (often in fear or awe).
In this usage, '戦く' conveys an internal feeling of fear or nervousness that the subject is attempting to control while acting.
戦く心を抑えながら、一歩踏み出した。
Suppressing his trembling heart, he took a step forward.
Here, the word '戦く' is used to show the subject's reaction of sudden fear or fright due to an external stimulus.
彼は雷の音に戦きました。
He was startled by the sound of thunder.
In this sentence, '戦く' describes a collective emotional reaction of fear or dread caused by witnessing something shocking or frightening.