From G1909 (epi) and G530 (hapax). An intensified form meaning 'once for all' β a single, unrepeatable, decisive act.
Ephapax is theologically decisive. In Romans 6:10, 'He died unto sin once.' Hebrews 7:27: Christ offered Himself 'once for all.' Hebrews 9:12: He entered the holy place 'once for all' with His own blood. The word eliminates any notion that Christ's sacrifice needs supplementing or repeating. It is finished. Ephapax is the adverb of the atonement.