Mat 5:22 But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool,G3474 shall be in danger of hell fire.
2Co 11:23 Are they ministers of Christ? (I speak as a fool G3912) I am more; in labours more abundant, in stripes above measure, in prisons more frequent, in deaths oft.
Probably form the base of G3466; dull or stupid (as if shut up), that is, heedless, (morally) blockhead, (apparently) absurd: - fool (-ish, X -ishness).
I like language studies but with this word it has no built in repugnant meaning that we can discern through translation by historical usage. Its not the equivalent of the f word or anything as far as I know.
This is my favorite kind of Bible problem one in which only Christ himself can solve. I do not claim to be him but I have this really kool recording of all the stuff I need for life in Christ called the Bible. There are other words fool used in the new testament and they are simular but they are not this exact word so its impossible to tell if they are equivocal unless they are used in a contextual exchange within reference texts of the Gospels.
With the Bible you cross reference the greek word and use its context to explain what this word fool which we are never supposed to say actually means and it turns out its close to Godless abomination.
The first rule of this kind of cross reference is that you discern who Chris is speaking to. Here it was Jews. He would have prolly been speaking in aramaic with some kind of hebrew mix. That doesn't really matter what matters is that we need to cross reference into the Old Testament.
Psa 14:1 To the chief Musician, A Psalm of David. The fool hath said in his heart, There is no God. They are corrupt, they have done abominable works, there is none that doeth good.
The Old Testament describes this word or something simular to it as the equivalent of atheist but it adds abominable and without good. You can read pure evil as a translation.
Now that we understand how the word might have resonated with the crowd we can move forward into what the word actually means in the mind of Christ.
Mat 7:24 Therefore whosoever heareth these sayings of mine, and doeth them, I will liken him unto a wise man, which built his house upon a rock:
Mat 7:25 And the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell not: for it was founded upon a rock.
Mat 7:26 And every one that heareth these sayings of mine, and doeth them not, shall be likened unto a foolish man, which built his house upon the sand:
Mat 7:27 And the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell: and great was the fall of it.
Here Jesus specificly says the person who is a fool is the one who refuses to do them but hears them anyways. A person who is stubborn against God.
Pro 29:1 He, that being often reproved hardeneth his neck, shall suddenly be destroyed, and that without remedy.
Jesus was referring to the man of Prov 29 who had been corrected through and by the word and those who represent the Word but refused to heed Godly counsel knowing full well it was Godly counsel. This isn't the person who questioned the validity of the teacher or the person who doubted that it was God. This is the person who knows its God yet turns away anyways.
So the equivalent translation of the word fool based on crossrfferencing is:
There is no hope you! You abomination! You never should have been born! You're destined for hell! Your stupid and moronic! You refuse to listen to anyone! You're going to burn for it! (then some cuss words too)