Like I said, hanging onto a fine thread is not how to study God's Word. Good grammar also includes staying in the context of what is being said; it's called 'reading comprehension' in English.
I Jn 2:18
18 Little children, it is the last time: and as ye have heard that antichrist (Greek antichristos) shall come, even now are there many (Greek polloi) antichrists (Greek antichristoi); whereby we know that it is the last time.
(KJV)
The first "antichrist" John mentioned is Greek antichristos (antichrist-singular), made up of two Greek words, anti (against or instead of) and Christos (Christ). Note it does not have Greek polli (many) in front of it like that latter antichristoi (antichrists-plural) does. That's why the first time John used the word "antichrist" it's singular.
But who would want to hang a whole doctrine just on that, since context is just as important as the Greek tense? And what about other Bible witnesses of John's comparison regarding that verse? For every Truth in God's Word there will always be at least two witnesses.
The other 3 examples John gives in 1 John 2:22; 1 John 4:3; and 2 John 1:7 help, but only declare antichrist to be anyone who denies The Father and The Son and that Christ came in the flesh. That of course includes Satan, for he was the first to deny The Father and The Son, which is what the first sin was about when he first rebelled against God in coveting His Throne. Satan's sin was in wanting to be God, and wanting to be worshipped in place of God.
Apostle Paul gave another witness to what John said in that 1 John 2:18 verse...
2 Thess 2:6-11
6 And now ye know what withholdeth that he might be revealed in his time.
7 For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way.
That is the same subject John was speaking in 1 John 2:18 about "many antichrists" (polloi antichristoi) that "even now there are many" as compared to a singular "antichrist" (antichristos) "that shall come".
Just who is that "he" that Paul says "that he might be revealed in his time"? It's the one Paul warned of back in the 2 Thess.2:3-4 verses...
2 Thess 2:3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
(KJV)
Notice the tense of that particular "he". It's singular. What that false one is to do is a very, very specific type of working, the SAME type of false working Satan did in the beginning when he first rebelled against God in coveting His Throne (Ezek.28; Isaiah 14).
Do you know what those on the 'many antichrists' only tradition of man want you to do with Paul's warning there? They want you to now go totally against the Greek tense of that singular false one in 2 Thess.2, and say that only means 'many'. They want you to replace all those words I underlined that Paul spoke with the idea of 'many'. How amazing it is they want you to change the tense to instead say, 'many sons of perdition', 'many men of sin', 'they' instead of "himself", and 'they' instead of "he".
8 And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of His mouth, and shall destroy with the brightness of His coming:
9 Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
10 And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.
11 And for this cause God shall send them strong delusion, that they should believe a lie:
(KJV)
PAUL IS WARNING OF A SPECIFIC FALSE ONE...
with "that Wicked", not many. The KJV translators even capitalized "Wicked" to let us know they understood Paul spoke of what, 'many'? or a singular Wicked one? The word "Wicked" is capitalized to show it applied as a PRONOUN. It's used as a title here for a specific person. The word "that" (Greek ho) makes it specifically singular.
So what about that "strong delusion" Paul links to "that Wicked" causing many to fall prey to "a lie"? What lie would cause many to fall away from Christ to that strong delusion of "that Wicked" one? What kind of working is that Paul said, with that Wicked coming to exalt himself over all that worshipped, so that he as God will sit in the temple of God, showing himself that he is God?
Now we're back to the first Greek word 'antichristos' John used (which is singular in the Greek with no modifier like polloi). The Greek word 'antichristos' can mean 'against Christ' or 'instead of, or in place of Christ'. Which meaning of that word would apply here from Paul's warning? Paul's warning is definitely about the idea of an "instead of or in place of Christ'.
WHAT LEVEL OF FALSE WORKING...
is that 'instead of or in place of Christ' to do? Paul shows us with, "after the working of Satan with all power and signs and lying wonders". The word "after" means 'according to' in the Greek. With "all power" of Satan? What man has ever had that?!?
Do you know what that Greek word for that "power" (dunamis) means? Look it up in your Strong's if you doubt me. It's the same Greek word used to describe miraculous power, like God's Power. That's a very specific idea Paul gave there. He's pointing to a level of miracle working on this earth that only God could do, like what our Lord Jesus did. Paul is letting us know that antichrist that shall come is not about many flesh men claiming to be Christ. It's about a man that will actually perform great miracles on the earth in the sight of men, and miraculous wonders and signs that would if possible, almost deceive Christ's own elect (remember Matthew 24:23-24?). In that 2 Thess.2:11 verse, Paul is showing us God is Who is sending that false one to work 'dunamis' on the earth. God is going to allow that false one to have that kind of power to deceive with, and it's meant for those who have not a love for His Truth in His Word.
DIDN'T OUR LORD JESUS WARN OF A DRAGON COMING TO WORK MIRACLES...
on the earth in the sight of men (given through His servant John)? YES!!!
Rev 13:11-14
11 And I beheld another beast coming up out of the earth; and he had two horns like a lamb, and he spake as a dragon.
Who is The Lamb? The True Lamb is our Lord Jesus, The Lamb Slain. But not this particular lamb here, for this one spake as a dragon while only appearing LIKE a lamb. Does that have anything to do with that "antichrist" (antichristos) definition of 'instead of or in place of Christ'? Most definitely yes! And who is the "dragon" per God's Word? Per Rev.12:9 and 20:2 the "dragon" is another title for Satan himself (look it up if you doubt me). That kind of explains why this dragon here comes "up out of the earth", doesn't it? That's a metaphor for Satan ascending up from the bottomless pit, like the one of Rev.11:7.
12 And he exerciseth all the power of the first beast before him, and causeth the earth and them which dwell therein to worship the first beast, whose deadly wound was healed.
13 And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,
14 And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast; saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.
(KJV)
Wow! That's the same kind of false working with miracles which Paul mentioned in 2 Thess.2 isn't it? Yes. It's also the same kind of miracle working used to deceive that our Lord Jesus also warned us of in Matt.24:24.
THAT is how we are to study God's Word. We are not to hang on a sole word from God's Word like "antichrist", but instead allow God's Word to interpret Itself.