c.1330,
rascaile "people of the lowest class, rabble of an army," from O.Fr.
rascaille "outcast, rabble" (12c.), perhaps from
rasque "mud, filth, scab, dregs," from V.L.
*rasicare "to scrape" (see
rash (n.)). The singular form is first attested 1461; extended sense of "low, dishonest person" is from early 1586.