Commentaire sur Rois 1 8:2

In the month Eisonim. [Targum] Yonoson rendered, “In the month which people of the ancient times called the first month, on the festival, and at present it is the seventh month,” i.e., since the Torah was given, and it is written in the month of Nissan which it is the first of the months, [therefore,] Tishrei³Although the construction of the Beis Hamikdosh was completed in the eighth month of the previous year [see above 6:38], Shlomo postponed its dedication until the following Tishrei. is called the seventh [month].⁴איתן means “mighty” and ירח האיתנים refers to the month of Tishrei which has the strongest spiritual effect for people to improve themselves because of the holidays celebrated during Tishrei—Ralbag. Alternatively, איתנים alludes to the Patriarchs. See Maseches Rosh Hashana 11a.