Varunam

I wonder if anyone could help me with analysing the Sankskrit word pAzADhyA (Itrans). It is one of the names in Lalita sahasranama. As far as I know, the translation should be 'she that holds a noose.' There is the Sanskrit masculine word pAza, which means noose and there is the verb root dhi, which means holding. So it is possibly a root verb in the end, but I don't understand how you get from the form dhi to dhyA and how the dh become the retroflex Dh.