Filth

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Old English fȳlth ‘rotting matter, rottenness’, also ‘corruption, obscenity’, of Germanic origin; related to Dutch vuilte, also to foul.

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From Middle English filth, from Old English fȳlþu, from Proto-West Germanic *fūliþu, equivalent to foul +‎ -th.

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filth (n.)

Old English fylð "uncleanness, impurity, foulness," from Proto-Germanic *fulitho (source also of Old Saxon fulitha "foulness, filth," Dutch vuilte, Old High German fulida), noun derivative of *fulo- "foul" (see foul (adj.)). A classic case of i-mutation.