In language, an archaism (from the Ancient Greek: ἀρχαϊκός, archaïkós, 'old-fashioned, antiquated', ultimately ἀρχαῖος, archaîos, 'from the beginning, ancient') is the use of a form of speech or writing that is no longer current.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 occur only in certain fixed expressions (for example 'be that as it may') are not considered to be archaisms.

Archaisms are most frequently encountered in poetry, law, science, technology, geography and ritual writing and speech. Their deliberate use can be subdivided into literary archaisms, which seeks to evoke the style of older speech and writing; and lexical archaisms, the use of words no longer in common use. Archaisms are kept alive by these ritual and literary uses and by the study of older literature. Should they remain recognised, they can be revived, as the word anent was in this past century.