Eight, Eighteen, Eighth - Vine's Expository Dictionary of New Testament Words
Eight, Eighteen, Eighth
[ 1,,G3638, okto ]eight" (Lat., octo, octavus; cp. Eng., "octagon," "octave," "octavo," "October," etc.), is used in Luke 2:21; Luke 9:28; John 20:26; Acts 9:33; Acts 25:6; 1 Peter 3:20; in composition with other numerals, okto kai deka, lit., "eight and ten, eighteen," Luke 13:4, Luke 13:11, Luke 13:16; triakonta kai okto, "thirty and eight," John 5:5.
[ 2,,G3590, ogdoos ]
"eighth" (connected with the preceding), is used in Luke 1:59; Acts 7:8; 2 Peter 2:5; Revelation 17:11; Revelation 21:20.
[ 3,,G3637, oktaemeros ]
an adjective, signifying an "eighth-day" person or thing, "eight days old" (okto, and hemera, "a day"), is used in Philippians 3:5. This, and similar numerical adjectives not found in the NT, indicate duration rather than intervals. The Apostle shows by his being an "eighth-day" person as to circumcision, that his parents were neither Ishmaelites (circumcised in their thirteenth year) nor other Gentiles, converted to Judaism (circumcised on becoming Jews).