- extending back beyond memory, record, or knowledge: from time immemorial.
- originating in the distant past; ancient (postpositive in the phrase time immemorial)
c.1600, from French immémorial (16c.) “old beyond memory,” from Medieval Latin immemorialis, from assimilated form of in- “not, opposite of” (see in- (1)) + memorialis (see memorial). Something immemorial is ancient beyond memory; something immemorable is not memorable.
see time immemorial.