archaism

n. something characteristic of an earlier period; outmoded word or phrase; outmoded phenomenon

In language, an archaism is the use of a form of speech or writing that is no longer current. This can either be done deliberately (to achieve a specific effect) or as part of a specific jargon (for example in law) or formula (for example in religious contexts). Many nursery rhymes contain archaisms. Archaic elements that only occur in certain fixed expressions (for example "be that as it may") are not considered to be archaisms.
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Noun
1. the use of an archaic expression
(synonym) archaicism
(hypernym) formulation, expression
(derivation) archaize, archaise
(class) adust

(a.)
Antiquity of style or use; obsoleteness.
  

(a.)
An ancient, antiquated, or old-fashioned, word, expression, or idiom; a word or form of speech no longer in common use.
  

archaism