firmly instilled or established as if by heredity: the bred-in-the-bone integrity of the school's headmaster.
deeply committed or resolved; unwavering: a bred-in-the-bone believer in civil rights.
Origin of bred-in-the-bone
from the proverb “What is bred in the bone will not come out of the flesh,” first recorded in England (in Latin) circa 1290, widespread in various versions since the 15th cent.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019