'Hell' is just an English word made up to describe what Jesus says He is going to do to the unrepentant wicked. We can make up any word to try to describe the horrible fate of the unrepentant wicked that Jesus is going to punish them with. The real emphasis should be put on what Jesus warns the unrepentant wicked as to what He is going to do to them for all eternity. Simply stating that the English word 'hell' did not exist until 725 A.D. does not mean that hell, where Jesus damns the unrepentant wicked for all eternity, did not exist before this time.
NAB MAT 25:41
Then he will say to those on his left, 'Depart from me, you accursed, into the eternal fire prepared for the devil and his angels. For I was hungry and you gave me no food, I was thirsty and you gave me no drink, a stranger and you gave me no welcome, naked and you gave me no clothing, ill and in prison, and you did not care for me.' Then they will answer and say, 'Lord, when did we see you hungry or thirsty or a stranger or naked or ill or in prison, and not minister to your needs?' He will answer them, 'Amen, I say to you, what you did not do for one of these least ones, you did not do for me.' And these will go off to eternal punishment, but the righteous to eternal life." (ISA 58)
NAB2 LUK 16:19 The Rich Man and Lazarus
"There was a rich man who dressed in purple garments and fine linen and dined sumptuously each day. And lying at his door was a poor man named Lazarus, covered with sores, who would gladly have eaten his fill of the scraps that fell from the rich man's table. Dogs even used to come and lick his sores. When the poor man died, he was carried away by angels to the bosom of Abraham. The rich man also died and was buried, and from the netherworld, where he was in torment, he raised his eyes and saw Abraham far off and Lazarus at his side. And he cried out, 'Father Abraham, have pity on me. Send Lazarus to dip the tip of his finger in water and cool my tongue, for I am suffering torment in these flames.' Abraham replied, 'My child, remember that you received what was good during your lifetime while Lazarus likewise received what was bad; but now he is comforted here, whereas you are tormented. Moreover, between us and you a great chasm is established to prevent anyone from crossing who might wish to go from our side to yours or from your side to ours.' He said, 'Then I beg you, father, send him to my father's house, for I have five brothers, so that he may warn them, lest they too come to this place of torment.' But Abraham replied, 'They have Moses and the prophets. Let them listen to them.' He said, 'Oh no, father Abraham, but if someone from the dead goes to them, they will repent.' Then Abraham said, 'If they will not listen to Moses and the prophets, neither will they be persuaded if someone should rise from the dead.'"
NAB REV 22:12
"Remember, I am coming soon! I bring with me the reward that will be given to each man as his conduct deserves. I am the Alpha and the Omega, the First and the Last, the Beginning and the End! Happy are they who wash their robes so as to have free access to the tree of life and enter the city through its gates Outside are the dogs and sorcerers, the fornicators and murderers, the idol-worshipers and all who love falsehood."
The Blessed Mother's revelations on hell
The first part is the vision of hell.
Our Lady showed us a great sea of fire which seemed to be under the earth. Plunged in this fire were demons and souls in human form, like transparent burning embers, all blackened or burnished bronze, floating about in the conflagration, now raised into the air by the flames that issued from within themselves together with great clouds of smoke, now falling back on every side like sparks in a huge fire, without weight or equilibrium, and amid shrieks and groans of pain and despair, which horrified us and made us tremble with fear. The demons could be distinguished by their terrifying and repulsive likeness to frightful and unknown animals, all black and transparent. This vision lasted but an instant. How can we ever be grateful enough to our kind heavenly Mother, who had already prepared us by promising, in the first Apparition, to take us to heaven. Otherwise, I think we would have died of fear and terror.
We then looked up at Our Lady, who said to us so kindly and so sadly:
You have seen hell where the souls of poor sinners go. To save them, God wishes to establish in the world devotion to my Immaculate Heart. If what I say to you is done, many souls will be saved and there will be peace.