quail \kweyl, verb:

To lose heart or courage in difficulty or danger; shrink with fear.

She would have quailed in the same way if the armored bear had looked at her like that, because there was something not unlike Lorek in Will’s eyes, young as they were.
— Phillip Pullman, The Subtle Knife

I should have quailed in the absence of moonlight, for it was by the leading of stars only I traced the dim path; I should have quailed still more in the unwonted presence of that which tonight shone in the north, a moving mystery—the Aurora Borealis.
— Charlotte Brontë, Villette

The verb quail is not related to the more common noun. It comes from the Middle Dutch word quelen meaning “to suffer, be ill.” This sense of “to cower” was rare until the late 1800s.