"to lose heart, to shrink," mid-15c., of unknown origin, perhaps from M.Du. quelen
"to suffer, be ill," from P.Gmc. *kwel-
"to die" (see quell
). Or from obsolete quail
"to curdle" (late 14c.), from O.Fr. coailler
, from L. coagulare
). Sense of "cower" is attested from 1550s. Common 1520-1650, then rare until 19c.; apparently revived by Scott.