Here the ECF define "aionos" whether they intended to or not.
Tertullian Apology Part I XLV
No doubt about it, we, who receive our awards under the judgment of an all-seeing God, and who look forward to eternal punishment from Him for sin, — we alone make real effort to attain a blameless life, under the influence of our ampler knowledge, the impossibility of concealment, and the greatness of the threatened torment, not merely long-enduring but everlasting, fearing Him, whom he too should fear who the fearing judges, — even God, I mean, and not the proconsul.
Tertullian defines "aionos" as opposite "long enduring."
Polycarp Epistle to the Philippians
And, looking to the grace of Christ, they despised all the torments of this world, redeeming themselves from eternal punishment by [the suffering of] a single hour. For this reason the fire of their savage executioners appeared cool to them. For they kept before their view escape from that fire which is eternal and never shall be quenched, and looked forward with the eyes of their heart to those good things which are laid up for such as endure; things “which ear hath not heard, nor eye seen, neither have entered into the heart of man,” (1Co_2:9) but were revealed by the Lord to them, inasmuch as they were no longer men, but had already become angels.
Here Tertullian defines "ainios fire" as fire that never shall be quenched.
Ignatius The Epistle of Ignatius to the Romans. Chapter 3[student of John]
I desire the bread of God, the heavenly bread, the bread of life, which is the flesh of Jesus Christ, the Son of God, who became afterwards of the seed of David and Abraham; and I desire the drink of God, namely His blood, which is incorruptible love and eternal life.
Here Ignatius defines "aionios" as "eternal" by pairing it with "incorruptible love."
The First Apology of Justin Chap XIII
For they proclaim our madness to consist in this, that we give to a crucified man a place second to the unchangeable and eternal God, the Creator of all; for they do not discern the mystery that is herein, to which, as we make it plain to you, we pray you to give heed.
Here Justin defines "aionios" as "eternal" by pairing it with "unchangeable."
Irenaeus Against Heresies. Book IV. Chap XX [student of Polycarp, student of John]
5. For God is powerful in all things, having been seen at that time indeed, prophetically through the Spirit, and seen, too, adoptively through the Son; and He shall also be seen paternally in the kingdom of heaven, the Spirit truly preparing man in the Son66 of God, and the Son leading him to the Father, while the Father, too, confers [upon him] incorruption for eternal life, which comes to every one from the fact of his seeing God.
Here Justin defines "aionios" as "eternal" by pairing it with "incorruption."
Justin Martyr The First Apology of Justin. Chap VIII
This, then, to speak shortly, is what we expect and have learned from Christ, and teach. And Plato, in like manner, used to say that Rhadamanthus and Minos would punish the wicked who came before them; and we say that the same thing will be done, but at the hand of Christ, and upon the wicked in the same bodies united again to their spirits which are now to undergo everlasting punishment; and not only, as Plato said, for a period of a thousand years.
Here Justin defines "aionos" as "eternal" by contrasting it with "a thousand years."
Irenaeus Against Heresies. Book IV.Chap VI[student of Polycarp, student of John]
5. And for this purpose did the Father reveal the Son, that through His instrumentality He might be manifested to all, and might receive those righteous ones who believe in Him into incorruption and everlasting enjoyment (now, to believe in Him is to do His will); but He shall righteously shut out into the darkness which they have chosen for themselves, those who do not believe, and who do consequently avoid His light.
Here Justin defines "aionos" as "eternal" by pairing it with "incorruption."
Theophilus to Autolycus.Book I. Chap XIV
To those who by patient continuance in well-doing (Rom_2:7) seek immortality, He will give life everlasting, joy, peace, rest, and abundance of good things, which neither hath eye seen, nor ear heard, nor hath it entered into the heart of man to conceive.
Here Theophilus defines "ainios" by pairing it with "inmortality."
Athenagoras A Plea for the Christians.Chap. X. –
That we are not atheists, therefore, seeing that we acknowledge one God, uncreated, eternal, invisible, impassible, incomprehensible, illimitable, who is apprehended by the understanding only and the reason, who is encompassed by light, and beauty, and spirit, and power ineffable,by whom the universe has been created through His Logos, and set in order, and is kept in being.
Here Athenagorus defines "aionios" as "eternal by pairing it with "uncreated, invisible, impassible, incomprehensible, illimitable." That should be enough adjectives to convince anyone.
Clement of Alexandria The Instructor. [Paedagogus.] Book I.
Wherefore also the Scripture says, “The law was given through Moses,” (Joh_1:17) not by Moses, but by the Word, and through Moses His servant. Wherefore it was only temporary; but eternal grace and truth were by Jesus Christ.
Here Clement defines "aionios" as eternal by contrasting it with "only temporary."
Clement of Alexandria The Stromata, Or Miscellanies. Book I.
Chap. I. “Labour,” says the Lord, “not for the meat which perisheth, but for that which endureth to everlasting life.” (Joh_6:27)
Here Clement defines "aionios" by contrasting it with "meat that perishes."
Clement of Alexandria Second Epistle Chap VI
For if we do the will of Christ, we shall find rest; otherwise, nothing shall deliver us from eternal punishment, if we disobey His commandments. For thus also saith the Scripture in Ezekiel, “If Noah, Job, and Daniel should rise up, they should not deliver their children in captivity.” (Eze_14:14, Eze_14:20) Now, if men so eminently righteous are not able by their righteousness to deliver their children, how239 can we hope to enter into the royal residence 240 of God unless we keep our baptism holy and undefiled?
Here Clement defines "aionos" as "eternal" by saying "nothing shall deliver [the unrighteous] from "ainios punishment."
Tertullian Part First — Apologetic Chap XLV
On this ground Epicurus makes light of all suffering and pain, maintaining that if it is small, it is contemptible; and if it is great, it is not long-continued. No doubt about it, we, who receive our awards under the judgment of an all-seeing God, and who look forward to eternal punishment from Him for sin, — we alone make real effort to attain a blameless life, under the influence of our ampler knowledge, the impossibility of concealment, and the greatness of the threatened torment, not merely long-enduring but everlasting, fearing Him, whom he too should fear who the fearing judges, — even God, I mean, and not the proconsul.
Here Tertullian defines "aionos" by contrasting it with "not merely long enduring."