archaisms

noun
  1. 1

    The adoption or imitation of archaic words or style.

  2. 2

    An archaic word, style, etc.

    โ€œIn this text, the word "methinks" appears to be a deliberate archaism.โ€

Source: https://en.wiktionary.org/wiki/archaism, https://en.wiktionary.org/wiki/archaisms