"Archaic" is a word that describes something that is very old and no longer in common use. It is still a perfectly valid and commonly used word in the English language.
Examples of how "archaic" is used:
* "The castle is built in an archaic style."
* "The old man spoke in an archaic dialect."
* "The archaic laws were finally repealed."
However, if you are asking about a specific phrase that you think might be archaic, please provide the phrase and I can help you determine if it is indeed outdated.