(full) assurance

Concise Bible Dictionary:

This word has in the Old Testament a different application from that which it has in the New Testament In the former it is “confidence or trust,” and agrees with the hopes of God’s earthly people in connection with the security in which Israel will dwell when restored to their land, when all their enemies shall have been put down by divine power: the effect of righteousness will be “quietness and assurance forever,” (Isa. 32:1717And the work of righteousness shall be peace; and the effect of righteousness quietness and assurance for ever. (Isaiah 32:17)): whereas in their disobedience they should fear day and night and have no assurance of their life (Deut. 28:6666And thy life shall hang in doubt before thee; and thou shalt fear day and night, and shalt have none assurance of thy life: (Deuteronomy 28:66)).
In the New Testament the Greek word πληροφορἰα implies “full assurance” and refers to eternal salvation. The gospel reaches a soul in power, and in the Holy Ghost and in “much full assurance” (1 Thess. 1:55For our gospel came not unto you in word only, but also in power, and in the Holy Ghost, and in much assurance; as ye know what manner of men we were among you for your sake. (1 Thessalonians 1:5)). We also meet with:
2. the full assurance of hope (Heb. 6:1111And we desire that every one of you do show the same diligence to the full assurance of hope unto the end: (Hebrews 6:11)), issuing in continued diligence of the saints in their work and labor of love: and

Strong’s Dictionary of Greek Words:

Number:
4136 (find all occurrences in KJV Bible)
Greek:
πληροφορία
Transliteration:
plerophoria
Phonic:
play-rof-or-ee’-ah
Meaning:
from 4135; entire confidence
KJV Usage:
(full) assurance