[Formendacil]

Of course, one can take this question further, since, in the context it was originally posed, it dealt with Sauron as the Necromancer--in Mirkwood. And, as noted, this is being used as Sauron's name/title, as separate from his history as Sauron because his identity, as Sauron, was not known (at least for some time) to the West.

Any speculation dealing with the broader case of Sauron being a necromancer is interesting--and probably worth pursuing--but let's not forget that most of the reasons we might come up with for thinking "necromancer" an appropriate cognomen for Sauron are divorced from his hidden identity in Mirkwood. Anything to do with the Ringwraiths is out, on that score, because the Úlairi (Ringwraiths) are clearly known to be Sauron's doing at the time of the Last Alliance (cf. "Of the Rings of Power and the Third Age"). Consequently, the actions of the Witchking, Angmar in general, and the retaking of Minas Morgûl would not have been laid at Sauron's door when he was first named the Necromancer--and this would include the Barrow-wights of Cardolan.

William Cloud Hicklin has a good argument from the OED that Tolkien did not mean much of a reference to death, but merely a generally malevolent practicer of dark arts, but it would still be interesting to know what these dark arts are.

Also--it occurs to me that I am assuming it was the West that gave Sauron-in-Mirkwood the name/title "the Necromancer" but I'm not sure this is warranted on my part. Although, on the one hand, I seem to recall (but cannot readily find a passage that says so...) that Sauron either never could or never did assume fair form again after the fall of Númenor, this does not mean that Sauron would necessarily have put out so dark an image as to call himself the Necromancer--especially given that there are reasons, namely the quote from "Laws and Customs of the Eldar" that would suggest that such a name might have rung a few alarm bells in the memories of Wise had Sauron claimed it for himself.

But if Sauron DIDN'T take that title to himself, what DID he call himself when he first returned to Mirkwood?