I don't know if "antique" is the right word to describe whatever form of
Adunaic it was the Faithful spoke. Adunaic fell out of favor among them for
political reasons: The King's Men, the political enemies of the Faithful,
wanted to do away with the traditional Elvish influence on Numenor, and
therefore dispensed with Sindarin and spoke only Adunaic - a Mannish language.
When the Faithful established Arnor and Gondor, they found that Adunaic in
Middle-Earth had mutated from the pure form spoken in Numenor to a vernacular
with a heavy influx of words from other languages - thus, Westron or Common
Speech. The Faithful didn't hold pure Adunaic in much esteem for obvious
political reasons, and since everyone was already speaking Westron they didn't
bother to preserve a pure form of it. By the time of the War of the Ring I
doubt many people even remembered the original Adunaic
language.
