In fact, the noun in the nominative singular, is χιλιάς which is feminine. This is a "group" of a thousand. In fact, that is the word used in Luke 14:31; Acts 4:4; Rev. 7:4-8, 11:13, 14:1 and 21:16.
The word used in the above verses in Revelation, is an adjective, not a noun. It's lexical form is:
χίλιοι, αι, α
Quite simply, it is a word that describes "year" or ἔτη, such as in verses 20:2, 3, 4, 5, 6, 7!
So, in fact, there is NO "The Millennium" at all in Rev. 20. All those words, as you so aptly have illustrated, Stephen, are adjectives.
And just for reference, there are two lexical forms of the word in BDAG. None of them are the forms you give above. Again, they are χιλιάς and χίλιοι. And if you want to be correct, χίλια is in the accusative case, in all the times it appears in Rev. 20.And for reference, Χιλίων is genitive plural, χιλίας is genitive singular. So, your occurrences are not different words, just in different cases.
And in fact, you are also wrong in Rev. 20 about the word not being plural. The word years or ἔτη is accusative plural, feminine, which is why the adjective must be accusative feminine plural. So, it is PLURAL in the example in Rev. 20. Because it describes a plural noun. The adjective must agree with the word it describes in Greek, German, French, Spanish, etc. Only English fails to note that distinction.
So, once again, a little bit of knowledge, and reading Strong's, instead of knowing Greek and using Bauer (BDAG) results in some wrong interpretation.
However, you were right to call me on my last statement. I was meaning, that this so-called "thousand year millennium" (rather redundant, since a millennium means thousand!) In which Jesus will set up his Kingdom, and then be overcome by the devil. Because, if Jesus is ruling and reigning, I don't believe things will ever fall apart. The devil will be gone, overthrown forever when Jesus returns.
But getting back to the use of "thousand," for example, 2 Peter 3:8, is NOT talking about the Millennial reign, but rather using the word "thousand" to be a definite, literal period of time, but rather, thousand represents the eternity of God.
"Now, dear friends, do not let this one thing escape your notice, that a single day is like a thousand years with the Lord and a thousand years are like a single day." 2 Peter 3:8
That is what I meant, although I realize it did not come across that way, which is on me!