Adjective ogdoos (eighth) in the New Testament

(Translation from NRSV for the New Testament with a few modifications for a more litteral meaning)

Luke

1: 59On the eighth (ogdoos) day they came to circumcise the child, and they were going to name him Zechariah after his father.

Acts

7: 8Then he gave him the covenant of circumcision. And so Abraham became the father of Isaac and circumcised him on the eighth (ogdoos) day; and Isaac became the father of Jacob, and Jacob of the twelve patriarchs.

2 Peter

2: 5and if he did not spare the ancient world, he preserved eighth (ogdoos) with Noah, a herald of righteousness, with seven others, when he brought a flood on a world of the ungodly;

Revelation

17: 11As for the beast that was and is not, it is an eighth (ogdoos) but it belongs to the seven, and it goes to destruction.
21: 20the fifth onyx, the sixth carnelian, the seventh chrysolite, the eighth (ogdoos) beryl, the ninth topaz, the tenth chrysoprase, the eleventh jacinth, the twelfth amethyst.