Etymology
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grain (n.)
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.
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grained 
in compounds, "having grains" (of a specified kind), 1520s; see grain (n.).
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grogram (n.)

coarse, stiff textile fabric, 1560s, from French gros grain "coarse grain or texture;" see gross (adj.) + grain (n.).

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grainy (adj.)
1610s, "full of grains," from grain + -y (2). Photographic sense is from 1900. In Middle English, grain also was used as an adjective, "like grain, lumpy, spotted" (early 15c.). Related: Graininess.
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granulose (n.)
part of starch convertible into sugar, 1874, coined in German by Swiss botanist Carl Nägeli (1817-1891) from Late Latin granulum "granule, small grain," diminutive of granum "grain" (see grain) + chemical suffix -ose (2).
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engrain (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.
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*gre-no- 
*grə-no-, Proto-Indo-European root meaning "grain."

It forms all or part of: corn (n.1); filigree; garner; garnet; grain; granary; grange; granger; granite; granular; granule; grenade; grenadine; kernel; pomegranate.

It is the hypothetical source of/evidence for its existence is provided by: Latin granum "seed," Old Church Slavonic zruno "grain," Lithuanian žirnis "pea," Old English corn.
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gravy (n.)

late 14c. (early 14c. in Anglo-French), from Old French grave, graue, apparently a misspelling of grané "sauce, stew," with -n- misread for -u- — the character used for -v- in medial positions in words in medieval manuscripts. The French word probably originally meant "properly grained, seasoned," from Latin granum "grain, seed" (see grain (n.)).

The meaning "money easily acquired" is attested by 1910; gravy train (by 1899) as something lucrative or productive is said to have been originally railroad slang for a short haul that paid well. Gravy-boat "small, deep dish for holding gravy or sauce" is from 1827.

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granule (n.)
1650s, from French granule or directly from Late Latin granulum "small grain," diminutive of Latin granum "grain," from PIE root *gre-no- "grain."
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granary (n.)
1560s, from Latin granaria (plural) "granary, store-house for grain," from granum "grain," from PIE root *gre-no- "grain."
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