Noun
Used other than figuratively or idiomatically: see black, mud.
Reduced mud found below the surface of sediments in lakes and rivers, the blackness of which is caused by the occurrence of metal sulphides.
Source: en.wiktionary.orgThere he lieth, tossing in the guilt of his lewdness, the primal lecher, neglectful of his duties to a fair wife but all too ready to plunge his sizzling steel into the slaking black mud of a base Indian. Anthony Burgess