'fallow' originates from Old English, specifically words like 'fealu' / 'fealg', which came from Proto-Germanic '*falwaz' meaning 'pale, yellowish'.

'fallow' changed from Old English words meaning 'pale, light brown/yellow' (compare Old High German 'falo', Old Norse 'falr') and in Middle English the term came to be used for plowed or unseeded land (perhaps by association with the pale color of such fields), eventually developing into the modern senses 'uncultivated' and 'inactive'.

Initially, it meant 'pale, yellowish' in reference to color; over time it evolved into its current primary meanings of 'uncultivated (land)' and more generally 'inactive or unused'.