Earnest (Noun) - Vine's Expository Dictionary of New Testament Words
Earnest (Noun)[ 1,,G728, arrabon ]
originally, earnest-money" deposited by the purchaser and forfeited if the purchase was not completed, was probably a Phoenician word, introduced into Greece. In general usage it came to denote "a pledge" or "earnest" of any sort; in the NT it is used only of that which is assured by God to believers; it is said of the Holy Spirit as the Divine "pledge" of all their future blessedness, 2 Corinthians 1:22; 2 Corinthians 5:5; in Ephesians 1:14, particularly of their eternal inheritance. In the Sept., Genesis 38:17-Genesis 38:18, Genesis 38:20. In modern Greek arrabona is an "engagement ring."