migratory game bird, 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, 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 be directly from Proto-Germanic. Slang meaning "young attractive woman" first recorded 1859.
c. 1400, "have a morbid craving;" early 15c., "grow feeble or sick;" mid-15c., "to fade, fail, give way," of unknown origin, perhaps from Middle Dutch quelen "to suffer, be ill," from Proto-Germanic *kwaljan (from PIE root *gwele- "to throw, reach," with extended sense "to pierce").
Or from obsolete quail "to curdle" (late 14c.), from Old French coailler, from Latin coagulare (see coagulate). Sense of "lose heart, shrink, cower" is attested from 1550s. According to OED, common 1520-1650, then rare until 19c., when apparently it was revived by Scott. Related: Quailed; quailing.