thoroughbred (adj.)

c. 1300, adjectival use of Old English þuruh (adv.) "from end to end, from side to side," stressed variant of þurh (adv., prep.); see through. Related: thoroughly; thoroughness.

Old English bredan "bring (young) to birth, procreate," also "cherish, keep warm," from West Germanic *brodjan (source also of Old High German bruoten, German brüten "to brood, hatch"), from *brod- "fetus, hatchling," from PIE root *bhreu- "to boil, bubble, effervesce, burn." The etymological notion is incubation, warming to hatch.

The intransitive sense "come into being" is from c. 1200; that of "beget or bear offspring" is from mid-13c. Of livestock, etc., "procure by the mating of parents and rear for use," mid-14c. The sense of "grow up, be reared" (in a clan, etc.) is late 14c.; the meaning "form by education" is from mid-15c. Related: Bred; breeding.