Anything immemorial is very, very old. You're most likely to hear this word in the phrase "time immemorial," a common way to say "so long ago that no one remembers it."

The French immémorial means "old beyond memory," from a Latin root. Don't confuse this adjective with immemorable, which is sometimes used instead, but which literally means "not worth remembering." Immemorial is a perfect way to describe ancient things, including stories, customs, religions, and even time itself.

Definitions of immemorial
  1. adjective
    long past; beyond the limits of memory or tradition or recorded history
    “time immemorial
    of long duration; not new
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