- mongrel (n.) late 15c., "mixed-breed dog," from obsolete mong "mixture," from O.E. gemong "mingling" (base of AMONG (Cf. among)), from P.Gmc. *mangjan "to knead together" (see MINGLE (Cf. mingle)). With pejorative suffix -REL (Cf. -rel). Meaning "person not of pure race" is from 1540s. As an adjective from 1570s.
Etymology dictionary. 2014.