fallow1 [Old English] In Old English the verb fealgian meant ‘to break up land for sowing’. Of Germanic origin, the word is related to Low German falgen. The sense now is ‘leave unsown’ referring to land which has been ploughed and harrowed.
fallow2 [Old English] Germanic in origin, Old English falu, fealu is related to Dutch vaal and German fahl, falb. Describing the colour pale brown or reddish yellow, it is now most commonly found in the word fallow deer, a Eurasian deer which has a reddish-brown coat in the summer.
– The Oxford Dictionary of Word Histories by Glynnis Chantrell