köken: From Middle High German vūl, from Old High German fūl, from Proto-West Germanic *fūl, from Proto-Germanic *fūlaz, from Proto-Indo-European *puH-lo-s (“rotten, putrid”). Compare Dutch vuil, English foul, Danish ful, Swedish ful. Doublet of Foul. The sense “lazy” developed in part from the idea of food rotting when lying around, in part from the notion that idleness is morally rotten.
aile: auf der faulen Haut liegen, faulen, Faulholzmotte, faulig, Fäulnis, Faultier, oberfaul, stinkfaul
köken: From Middle Dutch loy, from Proto-Germanic *lujaz. further etymology unsure. May be cognate with the Old Norse adjective lúinn (“exhausted”). Perhaps from Proto-Indo-European *lewH- (“to cut off, separate, free”), source of Proto-Germanic *lausaz, Albanian lirë.
aile: liever lui dan moe, luiaard, luibak, luie donder, luie stoel, luierik, luiheid, luilak, luilap, luilekker