1: αἰών
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(Strong's #165 — Noun Masculine — aion — ahee-ohn' )

"an age," is translated "eternal" in Ephesians 3:11 , lit., "(purpose) of the ages" (marg.). See AGE.

2: αἰώνιος
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(Strong's #166 — Adjective — aionios — ahee-o'-nee-os )

"describes duration, either undefined but not endless, as in Romans 16:25; 2—Timothy 1:9; Titus 1:2; or undefined because endless as in Romans 16:26 , and the other sixty-six places in the NT.

2—Corinthians 4:18Philemon 1:15Romans 16:261—Timothy 6:161—Peter 5:10Hebrews 9:14Hebrews 9:12Hebrews 5:92—Peter 1:11Luke 1:33John 3:16John 10:282—Corinthians 5:11—Corinthians 15:53Matthew 25:46Titus 1:2Mark 3:29Hebrews 6:2Matthew 18:825:41Jude 1:7Mark 9:432—Thessalonians 1:9
3: ἀΐδιος
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(Strong's #126 — Adjective — aidios — ah-id'-ee-os )

see EVERLASTING.