[hecht]

Some dictionaries now list the nonsense word “millenniums” to reflect its usage by the less educated. It is akin to dictionaries now listing “loan” as a verb. “Friends, Romans , countryman LOAN me your ears”

[decimon]

Some dictionaries now list the nonsense word “millenniums”...

Now list? That wasn't true, say, in the 1800s? You know that?

[RegulatorCountry]

Well, it actually can be used correctly, for entirely separate eras. A past millennium and a millennium to come, are collectively and correctly millenniums. Otherwise, it’s wrong.