A.T. Robertson Commentary 1 Corinthians 15:25

"For he must reign, till he hath put all his enemies under his feet." — 1 Corinthians 15:25 (ASV)

Till he hath put (αχρ ου θη). Second aorist active subjunctive of τιθημ, "till he put" (no sense in saying "hath put," merely effective aorist tense for climax. Αχρ (ου), μεχρ (ου), εως (ου) all are used for the same idea of indefinite future time.