'Reign' in the Bible

in the third year of his reign he held a banquet for all his officials and his attendants. The army officers of Persia and Media, the nobles and the officials of the provinces were there in his presence.

So Esther was taken to King Ahasuerus, to his royal palace in the tenth month, that is, the month of Tebeth (Dec-Jan), in the seventh year of his reign.