wet earth worked into a paste: mud, or the soft clay a potter shapes
This word names earth once water has been added to it, so that it holds together and can be smeared, kneaded, or shaped. Greek uses it both for the mud of a road or a riverbank and for the prepared material on a potter's bench, because these are the same stuff at different stages of usefulness.
In the New Testament it turns up in only two settings. Four times it is the paste Jesus makes on the ground and spreads on a blind man's eyes (John 9:6, 9:11, 9:14, 9:15). Once it is what a potter holds in his hands, free to make one pot for a place of honor and another for common use (Romans 9:21).
Neither passage is about a rare or costly substance. In John the point is that the healing runs through something as ordinary as wet dirt, and in Romans the point is that the material has no say in what it becomes. Older English Bibles render the John scenes with "clay", which can leave a reader picturing a craftsman's prepared material; the Greek asks for nothing more than mud.
Hebrew divides this ground between two words: the potter's clay (חֹמֶר) and the mud or mire of a street or a pit (טִיט). Greek covers both with this one word, while keeping a separate word for dry, loose dust (χόος).