mid-15c., "individual or breed of dog resulting from repeated crossings or mixture of several different varieties," from obsolete mong "mixture," from Old English gemong "mingling" (base of among), from Proto-Germanic *mangjan "to knead together" (source of mingle), from a nasalized form of PIE root *mag- "to knead, fashion, fit." With pejorative suffix -rel.
The distinction between a mongrel and a hybrid (a cross between two different breeds) is not always observed. Meaning "person not of pure race" is attested from 1540s. As an adjective, "of a mixed or impure breed," from 1570s.
It is the hypothetical source of/evidence for its existence is provided by: Greek magis "kneaded mass, cake," mageus "one who kneads, baker;" Latin macerare "soften, make soft, soak, steep;" Lithuanian minkyti "to knead;" Old Church Slavonic mazo "to anoint, smear;" Breton meza "to knead;" Old English macian "to make, form, construct, do," German machen "to make;" Middle Irish maistir "to churn."
"of two different colors, having spots or patches of white and black or another color," 1580s, formed from pie (n.2) "magpie" + bald in its older sense of "spotted, white;" in reference to the black-and-white plumage of the magpie. Hence, "of mixed character, heterogeneous, mongrel" (1580s). Properly only of black-and-white colorings (compare skewbald).
"offspring of a person of mixed blood," especially a person of mixed Spanish and Amerindian parentage," 1580s, from Spanish mestizo, Portuguese mestiço, "of mixed European and Amerindian parentage," from Late Latin mixticius "mixed, mongrel," from Latin mixtus "mixed," past participle of miscere "to mix, mingle" (from PIE root *meik- "to mix"). Fem. form mestiza is attested from 1580s. Compare mustee.
large, powerful breed of dog, apparently dating to ancient times, valued as a watch-dog, mid-14c., from Old French mastin "great cur, mastiff" (Modern French mâtin) or Provençal mastis, both of which probably are from Vulgar Latin *mansuetinus "domesticated, tame," from Latin mansuetus "tame, gentle" (see mansuetude). The etymological sense, then, would be a dog that stays in the house, thus a guard-dog or watchdog. The form in English perhaps was influenced by Old French mestif "mongrel."
c. 1300, blenden, "to mix in such a way as to become inextinguishable, mingle, stir up a liquid," in northern writers, from or akin to rare Old English blandan "to mix" (Mercian blondan) or Old Norse blanda "to mix," or a combination of the two; from Proto-Germanic *blandan "to mix," which comes via a notion of "to make cloudy" from an extended Germanic form of the PIE root *bhel- (1) "to shine, flash, burn."
Compare Old Saxon and Old High German blantan, Gothic blandan, Middle High German blenden "to mix;" German Blendling "bastard, mongrel," and, outside Germanic, Lithuanian blandus "troubled, turbid, thick;" Old Church Slavonic blesti "to go astray." Figurative sense of "mingle closely" is from early 14c. Related: Blended; blending.
Old English geolu, geolwe, "yellow," from Proto-Germanic *gelwaz (source also of Old Saxon, Old High German gelo, Middle Dutch ghele, Dutch geel, Middle High German gel, German gelb, Old Norse gulr, Swedish gul "yellow"), from PIE root *ghel- (2) "to shine," with derivatives denoting "green" and "yellow" (such as Greek khlōros "greenish-yellow," Latin helvus "yellowish, bay").
Occasionally in Middle English used of a color closer to blue-gray or gray, of frogs or hazel eyes, and to translate Latin caeruleus, glauco. Also as a noun in Old English. Meaning "light-skinned" (of blacks) first recorded 1808. Applied to Asiatics since 1787, though the first recorded reference is to Turkish words for inhabitants of India.
Yellow peril translates German die gelbe gefahr. Sense of "cowardly" is 1856, of unknown origin; the color was traditionally associated rather with jealousy and envy (17c.). Yellow-bellied "cowardly" is from 1924, probably a semi-rhyming reduplication of yellow; earlier yellow-belly was a sailor's name for a half-caste (1867) and a Texas term for Mexican soldiers (1842, based on the color of their uniforms). Yellow dog "mongrel" is attested from c. 1770; slang sense of "contemptible person" first recorded 1881. Yellow fever attested from 1748, American English (jaundice is a symptom).