noun

• (archaeology, US, usually capitalized) The prehistoric period intermediate between the earliest period (‘Paleo-Indian’, ‘Paleo-American’, ‘American‐paleolithic’, etc.) of human presence in the Western Hemisphere, and the most recent prehistoric period (‘Woodland’, etc.).
  "… Archaic Stage … the stage of migratory hunting and gathering cultures continuing into environmental conditions approximately those of the present."
• (paleoanthropology) (A member of) an archaic variety of Homo sapiens.
  "[...] prefer the third explanation for the advanced-looking features of Neandertals (Chapter 7) and the Ngandong hominins (Chapter 6), but they have had little to say about the post-Erectine archaics from China."

adj

• (chiefly lexicography, of words) No longer in ordinary use, though still used occasionally to give a sense of antiquity and are still likely to be understood by well-educated speakers and are found in historical texts.
  "The language of the Faerie Queene was made archaic Language:— in order to be in keeping with the chivalry of bygone ages that formed its subject."
• (archaeology) Belonging to the archaic period.