immemorial

As adjectives the difference between memorable and immemorial

is that memorable is memorable while immemorial is immemorial, age-old.

As a noun memorial

is memorial.

As an adjective immemorial is

immemorial, age-old.

As an adjective immemorial

is immemorial, age-old.

As a noun old is

age.

As adjectives the difference between antediluvian and immemorial

is that antediluvian is ancient or antiquated; old; prehistoric while immemorial is immemorial, age-old.

As a noun antediluvian

is one who lived prior to noah's flood.

As adjectives the difference between immemorial and solemn

is that immemorial is immemorial, age-old while solemn is deeply serious and somber.

As adjectives the difference between archaic and immemorial

is that archaic is of or characterized by antiquity; old-fashioned, quaint, antiquated while immemorial is immemorial, age-old.

As a noun archaic

is (archaeology|us|usually capitalized) a general term for the prehistoric period intermediate between the earliest period (‘[http://enwikipediaorg/wiki/paleo-indian paleo-indian]’, ‘paleo-american’, ‘american‐paleolithic’, &c ) of human presence in the western hemisphere, and the most recent prehistoric period (‘woodland’, etc).