Time immemorial is a term used to refer to a period of time that is so long ago that it cannot be remembered or measured. The crossword solutions for this term are ANTIQUITY (9 letters), EON (3 letters), EONS (4 letters), aeons (5 letters) and days of yore (10 letters). ANTIQUITY refers to a very old period of time, while an EON is an indefinite and very long period of time. EONS and aeons are both terms used to refer to a very long period of time, and days of yore is an expression used to refer to a distant past.