1. having no known beginning and presumably no end

- the dateless rise and fall of the tides

Similar word(s): infinite, endless, sempiternal

2. of such great duration as to preclude the possibility of being assigned a date

- dateless customs

Similar word(s): undatable

3. not bearing a date

- a dateless letter

Similar word(s): undatable, undated

4. unaffected by time

- few characters are so dateless as Hamlet

Similar word(s): unaltered, unchanged, timeless

Sentences with dateless as an adjective:

- They're so dateless that Burger King will not offer them a job.

- It is hard to believe that she could be dateless on a Saturday night.