Achri (ἄχρι) is a preposition and conjunction meaning "until, as far as, up to the point of." It marks a temporal or spatial limit. It appears approximately 48 times in the NT and is frequently used to mark pivotal eschatological turning points.
Achri is one of the NT's most theologically charged small words — it marks the boundary between the present age and the age to come. Key uses: Romans 11:25 — hardening upon Israel "until" the full number of Gentiles comes in; 1 Corinthians 11:26 — proclaiming the Lord's death "until" He comes; Revelation 2:25 — "hold on until I come." Every use in eschatological contexts encodes a promise: present conditions are temporary, bounded by God's sovereign 'until.' The darkness has a limit; the trial has a boundary; the exile has an end.