for ((n-))ever (lasting), old

Concise Bible Dictionary:

Three Hebrew words are translated “eternal.”
1. ad, very often translated “forever,” and with another word, olam, “forever and ever.” “The Lord shall reign forever and ever” (Ex. 15:1818The Lord shall reign for ever and ever. (Exodus 15:18)). “The Lord is king forever and ever” (Psa. 10:1616The Lord is King for ever and ever: the heathen are perished out of his land. (Psalm 10:16): Compare also Psa. 45:66Thy throne, O God, is for ever and ever: the sceptre of thy kingdom is a right sceptre. (Psalm 45:6); Psa. 48:1414For this God is our God for ever and ever: he will be our guide even unto death. (Psalm 48:14); Psa. 52:88But I am like a green olive tree in the house of God: I trust in the mercy of God for ever and ever. (Psalm 52:8); Mic. 4:55For all people will walk every one in the name of his god, and we will walk in the name of the Lord our God for ever and ever. (Micah 4:5)). Ad is also translated “everlasting:” “the everlasting Father,” or “Father of the everlasting age” (Isa. 9:66For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace. (Isaiah 9:6)). Also “eternity”; “the high and lofty One that inhabiteth eternity” (Isa. 57:1515For thus saith the high and lofty One that inhabiteth eternity, whose name is Holy; I dwell in the high and holy place, with him also that is of a contrite and humble spirit, to revive the spirit of the humble, and to revive the heart of the contrite ones. (Isaiah 57:15)).
5. αἰών “age, duration, ever.” With a preposition “unto the ages” is often translated “forever”; and, when repeated, “forever and ever.” “He that eateth of this bread shall live forever” (John 6:5858This is that bread which came down from heaven: not as your fathers did eat manna, and are dead: he that eateth of this bread shall live for ever. (John 6:58)). “Christ abideth forever” (John 12:3434The people answered him, We have heard out of the law that Christ abideth for ever: and how sayest thou, The Son of man must be lifted up? who is this Son of man? (John 12:34)). “To whom be glory forever and ever” (Gal. 1:55To whom be glory for ever and ever. Amen. (Galatians 1:5)). “According to the eternal purpose” (Eph. 3:1111According to the eternal purpose which he purposed in Christ Jesus our Lord: (Ephesians 3:11)). “Now unto the king honor and glory forever and ever” (1 Tim. 1:1717Now unto the King eternal, immortal, invisible, the only wise God, be honor and glory for ever and ever. Amen. (1 Timothy 1:17)). This word is often translated “world,” but may at times be better rendered “age,” as “be not conformed to this age” (Rom. 12:22And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God. (Romans 12:2)); and “forever and ever” may be translated “to the ages of ages,” though the meaning would be the same.
6. αἰώνιος, from αἰών, signifying “ever enduring.” It is always translated “eternal” or “everlasting,” except in Romans 16:2525Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began, (Romans 16:25), “since the world began,” or “in the times of the ages” (2 Tim. 1:99Who hath saved us, and called us with an holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the world began, (2 Timothy 1:9); Titus 1:22In hope of eternal life, which God, that cannot lie, promised before the world began; (Titus 1:2)); “before the world began,” or, “before the ages of time”; and Philemon 1:1515For perhaps he therefore departed for a season, that thou shouldest receive him for ever; (Philemon 15), “forever.” This word is applied to God Himself as “the everlasting God” (Rom. 16:2626But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith: (Romans 16:26)); to the Holy Spirit (Heb. 9:1414How much more shall the blood of Christ, who through the eternal Spirit offered himself without spot to God, purge your conscience from dead works to serve the living God? (Hebrews 9:14)); to redemption (Heb. 9:1212Neither by the blood of goats and calves, but by his own blood he entered in once into the holy place, having obtained eternal redemption for us. (Hebrews 9:12)); inheritance (Heb. 9:1515And for this cause he is the mediator of the new testament, that by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance. (Hebrews 9:15)); salvation (Heb. 5:99And being made perfect, he became the author of eternal salvation unto all them that obey him; (Hebrews 5:9)); glory (1 Peter 5:1010But the God of all grace, who hath called us unto his eternal glory by Christ Jesus, after that ye have suffered a while, make you perfect, stablish, strengthen, settle you. (1 Peter 5:10)); and constantly to life (John 3:15-16, 3615That whosoever believeth in him should not perish, but have eternal life. 16For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. (John 3:15‑16)
36He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him. (John 3:36)
). On the other hand it is applied to punishment (Matt. 25:4646And these shall go away into everlasting punishment: but the righteous into life eternal. (Matthew 25:46)); damnation (Mark 3:2929But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation: (Mark 3:29)); destruction (2 Thess. 1:99Who shall be punished with everlasting destruction from the presence of the Lord, and from the glory of his power; (2 Thessalonians 1:9)); and fire (Jude 77Even as Sodom and Gomorrha, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire. (Jude 7): Compare Isa. 33:1414The sinners in Zion are afraid; fearfulness hath surprised the hypocrites. Who among us shall dwell with the devouring fire? who among us shall dwell with everlasting burnings? (Isaiah 33:14)).
The above passages show that the same word is used for the existence of God Himself; for the salvation and blessedness of the saved; and for the punishment of the wicked.

Strong’s Dictionary of Hebrew Words:

(Aramaic) corresponding to 5769; remote time, i.e. the future or past indefinitely; often adverb, forever
KJV Usage:
for ((n-))ever (lasting), old