Strong's G3637 — ὀκταήμερος (adjective)
oktaemeros (ok-tah-ay'-mer-os) adj.
1. an eight-day old person or act
[from G3638 and G2250]
KJV: the eighth day 
Root(s): G3638, G2250 
Hebrew root: ἡμέρα
Occurrences: 1