Nameless Enemy

The people of Gondor, living in the shadow of Sauron's Dark Land of Mordor, would by tradition avoid using the Dark Lord's name, or indeed the name of the land where he dwelt. Instead, Sauron was typically referred to as the 'Nameless Enemy' or very often as simply the 'Enemy'. Other variations were also seen, so the Dark Lord might be the 'Nameless One' or the 'Unnamed', and his land the 'Nameless Land'. None of these terms imply that Sauron had no name - for indeed he had many - but simply that those names were not used by the Gondorians.

Boromir made the tradition explicit when he called Sauron 'him that we do not name',¹ but nowhere is it explained how this tradition emerged. It may simply be that the Gondorians disdained to use their ancient Enemy's name, or there may be a deeper implication. Historically it was believed that naming a powerful being could draw its attention to the speaker, and given Sauron's powerful and far-reaching Eye, that possibility was not entirely unrealistic. It's impossible to say whether the Gondorians literally feared drawing Sauron's Eye by speaking his name, but whatever its source, it is clear that they took this taboo seriously. Boromir, indeed, would not even use the name in Rivendell, hundreds of miles away from Sauron's Dark Tower.