ETYM Old Eng. auncien, French ancien, Late Lat. antianus, from Latin ante before. Related to Ante-, pref.
1. Belonging to times long past especially of the historical period before the fall of the Western Roman Empire.
2. Very old.
ETYM Pref. im- not + memorial: cf. French immémorial.
Long past; beyond the limits of memory or tradition or recorded history.
In an immemorial manner, beyond what can be remembered