Levy connects the Nahum passage with the root rwy and argues that the word literally renders Biblical ṭyṭ, thus "mortar" or the like. But the passage is clearly rendered metaphorically in the Targum, and such an interpretation ignores the parallel usage in the Isaiah passage. Note that it is always used with שעבד, i.e. control your slaves more as they work in the mud.
The unique Mandaic example may well be deemed a separate word, but we find no other form in the other dialects with which to connect it.