ingrain (v.)

also ingrain, late 14c., originally "dye (a fabric) red with cochineal," from French phrase en graine, from graine "seed of a plant," also "cochineal" (the source of the dye was thought to be berries), thus "fast-dyed." See grain; also compare kermes. Later associated with grain in the sense of "the fiber of a thing." Used figuratively from 16c. Related: Engrained.

"deeply rooted," 1590s, literally "dyed with grain "cochineal," the red dyestuff (see engrain). Figuratively, "thoroughly imbued" (of habits, principles, prejudices, etc.) from 1851. In reference to dyed carpets, etc., it is attested from 1766, from the manufacturing phrase in (the) grain "in the raw material before manufacture."