1. marked by the characteristics of an earlier period; antiquated: an archaic manner; an archaic notion.
2. (of a linguistic form) commonly used in an earlier time but rare in present-day usage except to suggest the older time, as in religious rituals or historical novels. Examples: thou; wast; methinks; forsooth.
3. forming the earliest stage; prior to full development: the archaic period of psychoanalytic research.