1.Definition: having no known beginning and presumably no end

"The dateless rise and fall of the tides"

Related Adjective(s):endless, sempiternal

2.Definition: not bearing a date

"A dateless letter"

Related Adjective(s):undated

3.Definition: of such great duration as to preclude the possibility of being assigned a date

"Dateless customs"

4.Definition: unaffected by time

"Few characters are so dateless as Hamlet"

Related Adjective(s):timeless