It's a matter of inadequate definitions in the dictionary reference. Tails is also called White Tie, and is even more formal than Black Tie, but both can be defined as evening wear. If I got that pairing, I would match wear, a more formal term than clothes, with tails, but it would still just be rationalising a 50-50 guess, and could be wrong.
(Editor in Humanities, Religion, Literature and Books For Children)
That's all, folks!