English keeps two different histories under the same spelling. In ordinary talk, fallow is the field left unsown after the plough, or a stretch of time when nothing is being produced. Naturalists still use the older color sense in the name of the fallow deer. Those meanings sit side by side in one modern word, but they come from two Old English ancestors that only later fell together in sound and spelling. The origin of the word fallow is that split, not a single line from one root.
What the word does now
The farming sense is the default. As a noun, fallow is ground that has been ploughed and harrowed yet left without seed for a season, and also the idle period itself. As an adjective it describes that land, and by a later figurative step a talent, a market, or a career that is unused but not finished. As a verb it means to put land into that state, breaking it so weeds die and moisture holds. None of this arrived through French or Latin. The word was already English in the Old English period, before 1150.
The color sense is narrower now. It once named a tawny, dusky, yellowish brown on horses, flame, withered grass, even water in verse. Today it is rare outside the deer, whose coat kept the old hue-word alive.
How the land word entered English
The agricultural noun continues Old English fealh, also written fealg and felg. It is inherited from West Germanic, not borrowed. In the earliest records it does not appear in farming manuals. It appears in glosses, where scribes used it for Latin occa. That lemma caused lasting trouble. In medieval Latin occa usually meant a harrow, so early readers took the Old English word as a tool. Later research, now the view of the major historical dictionaries, reads those glosses as ploughed, arable ground. The Latin in the relevant texts is likely a variant of Gaulish olca, arable land, rather than the harrow word. Almost every Old English citation sits in that gloss tradition, and several go back to Aldhelm’s prose.
Middle English is less cryptic. Forms such as falwe and falow name tilled land: the clods a rider might cross in Havelok and in Chaucer, or arable ground listed with pastures. The verb fallow continues Old English fealgian, to break up land, with kin in Dutch valgen and German Low German falgen.
The color adjective is a separate inheritance: Old English fealu, Middle English falwe. By late Old English the two words were close enough in sound that the land term was drawn toward the color word, probably because freshly turned earth looks pale brown. Spelling completed the merger. The deer name is the color word, not the field word.
Roots and relatives
West Germanic reconstructions for the land noun include falgu and close variants falgō- / falgjō-. Cognates are tightly agricultural: Old Frisian fallach, arable land; West Frisian felge; Dutch valg (older valge); Middle Low German valge; Old High German felga; regional German Falge, Felge, Falg for ploughed or fallow ground; East Frisian falge for fallow land and a related verb for breaking soil.
Deeper than Germanic, the path is probable, not settled. A reconstructed Indo-European polḱéh₂, arable land, would link the English noun with Gaulish olca (later French ouche, a plot of ground) and with Slavic words for a strip of field: Russian polosa, Polish płosa, Slovene plasa. Some scholars treat that noun as built on a verb meaning to turn or bend, the family sometimes also proposed for felloe, the rim of a wheel, as if both named things that turn. Other accounts prefer a root meaning to fold, hence to turn the soil. A few older dictionaries pointed at Greek polos, a ploughed field. None of those distant ties is agreed. What is firm is the West Germanic farming cluster and native inheritance into English.
The color adjective is cleaner at depth. It continues Germanic falwa- / falwaz, matching Old Saxon falu, Old Norse fölr, Dutch vaal, Old High German falo, and German falb and fahl. Behind them stands a wide Indo-European set of pale and gray words: Lithuanian palvas, Russian polovyj, Latin pallidus, Greek polios. Those cousins explain the deer. They do not explain the field.
From broken earth to rest
The land word changed sense more than form. In Old and early Middle English the core was ploughed or arable land, not a vacant season. When a medieval poet sends a rider over the falwes, the picture is broken ground. The specialized meaning land ploughed but left unsown is later. Standard dating puts that sense in the 1520s. The adjective for land left untilled after ploughing is recorded from the late fourteenth century. The figurative use follows: a mind or a skill can lie fallow, idle yet ready.
That shift tracks the technique. Leaving ground unsown after ploughing and harrowing restored fertility, killed weeds, and conserved moisture. As the practice became the named thing, the older general sense ploughed land faded and is now obsolete. A modern reader can miss how physical the Middle English noun was.
A deer, not a field
The concrete remainder is the homonym. Fallow deer do not take their name from idle acres. The animal keeps Old English fealu, the tawny color; the field keeps fealh, the arable noun. They met on the page because turned earth and a dun hide share a hue, not because they share a root. English had the land word before the twelfth century, still meaning broken ground. Only some centuries later did it narrow to the rest that farmers now mean by a fallow year.