Words and phrases that were used regularly in a language, but are now less common are archaic. Such words and phrases are often used deliberately to refer to earlier times. For instance, the pronoun 'thou', which is very rarely used nowadays is an archaism, which is sometimes used to suggest biblical language or a dialect.
See Also: Figure of speech
Browse the following links to other content related to the term 'Archaic Language' from the 'Varieties and Dialects' grammar category: