engrain v.

early 14c., "a small, hard seed," especially of one of the cereal plants, also as a collective singular, "seed of wheat and allied grasses used as food;" also "something resembling grain; a hard particle of other substances" (salt, sand, later gunpowder, etc.), from Old French grain, grein (12c.) "seed, grain; particle, drop; berry; grain as a unit of weight," from Latin granum "seed, a grain, small kernel," from PIE root *gre-no- "grain." From late 14c. as "a species of cereal plant." In the U.S., where corn has a specialized sense, it is the general word (used of wheat, rye, oats, barley, etc.).

Figuratively, "the smallest possible quantity," from late 14c. From early 15c. in English as the smallest unit of weight (originally the weight of a plump, dry grain of wheat or barley from the middle of the ear). From late 14c as "roughness of surface; a roughness as of grains." In reference to wood, "quality due to the character or arrangement of its fibers," 1560s; hence, against the grain (1650), a metaphor from carpentry: cutting across the fibers of the wood is more difficult than cutting along them.

Earliest sense of the word in English was "scarlet dye made from insects" (early 13c.), a sense also in the Old French collateral form graine; see kermes for the evolution of this sense, which was frequent in Middle English; also compare engrain. In Middle English grain also could mean "seed of flowers; pip of an apple, grape, etc.; a berry, legume, nut." Grain alcohol attested by 1854.

c. 1600, "shield louse (Coccus ilicis) that yields a red dye" (1590s of the tree on which the insects live), from Medieval Latin cremesinus (also source of French kermès, Italian chermes, Spanish carmes), from Arabic qirmiz "kermes," from Sanskrit krmi-ja a compound meaning "(red dye) produced by a worm."

The Sanskrit compound is krmih "worm" (from PIE root *kwrmi- "worm," source also of Lithuanian kirmis, Old Irish cruim, Albanian krimp "worm") + -ja- "produced" (from PIE root *gene- "give birth, beget"). The insect lives in the Levant and southern Europe on a species of small evergreen oak (kermes oak) and in ancient Europe were the main source of red and scarlet dye. The dye is prepared from the dried bodies of pregnant females, which alive resemble small roundish grains about the size of peas and cling immobile to the tree on which they live. From this fact kermes dye was, for a long time, mistaken as being from a seed or excrescence of the tree, and the word for it in Greek was kokkos, literally "a grain, seed" (see cocco-). This was passed to Latin as coccum, coccus "berry [sic] yielding scarlet dye," in late use "scarlet color, scarlet garment."

So important was kermes (coccus) as a commercial source of scarlet dye that derivatives of the name for it have displaced the original word for "red" in many languages, such as Welsh coch (from Latin), Modern Greek kokkinos. Also compare Russian čcermnyj "purple-red," Old Church Slavonic čruminu. Compare also crimson (n.).

Kermes dyes have been found in burial wrappings in Anglo-Scandinavian York, but the use of kermes dyes seems to have been lost in Europe from the Dark Ages until early 15c. It fell out of use again with the introduction of cochineal (the word for which itself might be from coccus) from the New World.

Cloths dyed with kermes are of a deep red colour; and though much inferior in brilliancy to the scarlet cloths dyed with real Mexican cochineal, they retain the colour better and are less liable to stain. The tapestries of Brussels and other parts of Flanders, which have scarcely lost any thing of their original brilliancy, even after a lapse of 200 years, were all dyed with kermes. [W.T. Brande, "Dictionary of Science, Literature, & Art," London, 1842]