Strong’s Greek
G1558 — ekdikos
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
ἔκδικος
ekdikos — pronounced ek'-dik-os
from 1537 and 1349; carrying justice out, i.e. a punisher:--a (re-)venger. see GREEK for 1537 see GREEK for 1349
2 occurrences in the KJV.
Romans 13:4
For he is the minister of God to thee for good. But if thou do that which is evil, be afraid; for he beareth not the sword in vain: for he is the minister of God, a revenger to execute wrath upon him that doeth evil.
1 Thessalonians 4:6
That no man go beyond and defraud his brother in any matter: because that the Lord is the avenger of all such, as we also have forewarned you and testified.