small migratory game bird of the Old World, late 14c. (early 14c. as a surname, Quayle), from Old French quaille (Modern French caille), perhaps via Medieval Latin quaccula (source also of Provençal calha, Italian quaglia, Portuguese calha, Old Spanish coalla), or directly from a Germanic source (compare Dutch kwakkel, Old High German quahtala "quail," German Wachtel, Old English wihtel), imitative of the bird's cry. Or the English word might have come up indigenously from Proto-Germanic.
Slang meaning "young attractive woman" is attested by 1859. Applied to similar birds in the New World.
Among such, the species of bob-white, as Ortyx virginiana, the common partridge or quail of sportsmen, are the nearest to the Old World species of Coturnix. In the United States, wherever the ruffed grouse, Bonasa umbella, is called pheasant, the bob-white is called partridge: where that grouse is called partridge, the bob-white is known as quail. [Century Dictionary, 1897]
c. 1400, "have a morbid craving;" early 15c., "grow feeble or sick, begin to die;" mid-15c., "to fade, fail, give way," probably from Middle Dutch quelen "to suffer, be ill," from Proto-Germanic *kwaljan (source also of Old Saxon quelan "to die," Old High German quelan "die," German quälen "suffer pain"), from PIE root *gwele- "to throw, reach," with extended sense "to pierce."
Or perhaps from obsolete quail "to curdle" (late 14c.), from Old French coailler, from Latin coagulare (see coagulate).
Sense of "lose heart or courage, shrink before a danger or difficulty, cower" is attested from 1550s. According to OED, the word was common 1520-1650, then rare until 19c., when apparently it was revived by Scott. Related: Quailed; quailing.