At the very.....
Literally: at the very essence of; precisely in the middle of; right in the midst of. (The primary origin of the expression is in the Bible, as in Exodus 12:51: “And it was on that very day that the Lord brought the children of Israel out of the land of Egypt according to their divisions.”)
(“And Moses said to the people: Remember this day—just as there it was at the very essence of the day, so here it is at the very essence of the day.” — Shabbat 86b.)
Translation
Expression (Hebrew)
בְּעִצּוּמוֹ שֶׁל...,בעיצומו של...
Definition (Hebrew)
מַמָּשׁ בָּאֶמְצַע שֶׁל..., בְּתוֹךְ... (מְקוֹרוֹ הָרִאשׁוֹנִי שֶׁל הַבִּטּוּי בַּתָּנָ"ךְ כְּמוֹ בַּפָּסוּק בִּשְׁמוֹת יב נָא: "וַיְהִי בְּעֶצֶם הַיּוֹם הַזֶּה הוֹצִיא ה' אֶת בְּנֵי יִשְׂרָאֵל מֵאֶרֶץ מִצְרַיִם עַל צִבְאֹתָם").
("וַיֹּאמֶר מֹשֶׁה אֶל הָעָם זָכוֹר אֶת הַיּוֹם הַזֶּה, מָה לְהַלָּן- בְּעִצּוּמוֹ שֶׁל יוֹם, אַף כָּאן - בְּעִצּוּמוֹ שֶׁל יוֹם"-שַׁבָּת פּוֹ ע"ב)