Greek: αμεμπτως [amemptôs] (Adverb). From αμεμπτος [amemptos]. Blamelessly. Irreproachably. Faultlessly.

αμεμπτως [amemptôs] appears 2 times in the NT:

(1) 1 Thessalonians 2: 10
Ye [are] witnesses, and God [also], how holily and justly and unblameably we behaved ourselves among you that believe:

(2) 1 Thessalonians 5: 23
And the very God of peace sanctify you wholly; and [I pray God] your whole spirit and soul and body be preserved blameless unto the coming of our Lord Jesus Christ.