the GNU version of the Collaborative International Dictionary of English
adj. Extending beyond the reach of memory, record, or tradition; indefinitely ancient.
The Century Dictionary and Cyclopedia
Not within the bounds of memory; of unknown duration; extending back beyond record or tradition.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adj. long past; beyond the limits of memory or tradition or recorded history
Word Usage
"The mountains rose, their debris silted up the ocean, the gods took their seats on them and contrived the river, and the India we call immemorial came into being."