on the same day/on the self-same day
That very day itself.
(“He shall purify himself with it on the third day and on the seventh day he shall be clean” (Numbers 19:12), and also: “On that very day, Rabbi Yehoshua ben Horkenus expounded: Job did not serve the Holy One Blessed Be He except out of love, as it is said (Job 13): ‘Though He slay me, yet will I trust in Him’” (Sotah 5:5), and also: “On that very day, when it became known to friends and acquaintances of the return of the Najara family... many came to greet them” (Y. Burla, Yearnings, p. 102), and also: “The question returns to its place: when was it? Was it on that very day, or the next?” (Agnon, A City and Its Fullness, p. 112), and also: “On that very day, after Havdalah, he presented himself before Rabbi Brishel and delighted him with Torah insights” (Ch. Haz, The First Generations, p. 22))
Translation
Expression (Hebrew)
בּוֹ בַּיּוֹם
Definition (Hebrew)
אוֹתוֹ הַיּוֹם עַצְמוֹ.
("הוּא יִתְחַטָּא בוֹ בַּיּוֹם הַשְּׁלִישִׁי וּבַיּוֹם הַשְּׁבִיעִי יִטְהָר"- בַּמִּדְבָּר י״ט י״ב, וְכֵן: "בּוֹ בַּיּוֹם דָּרַשׁ ר' יְהוֹשֻעַ בֶּן הוֹרְקְנוֹס: לֹא עָבַד אִיּוֹב אֶת הַקָּדוֹשׁ בָּרוּךְ הוּא אֶלָּא מֵאַהֲבָה שֶׁנֶּאֱמַר (אִיּוֹב י״ג) הֵן יִקְטְלֵנִי לוֹ אֲיַחֵל"- מַסֶּכֶת סוֹטָה ה׳ ה׳, וְכֵן: "בּוֹ בַּיּוֹם, כְּשֶׁנּוֹדַע לִידִידִים וּמוּדָעִים דְּבַר שׁוּבָהּ שֶׁל מִשְׁפַּחַת נַגָ'ארָה ...בָּאוּ רַבִּים לְהַקְבִּיל פְּנֵיהֶם"- י. בּוּרְלָא/ כִּסּוּפִים, 102, וְכֵן: "חוֹזֶרֶת הַשְּׁאֵלָה לִמְקוֹמָהּ, אֵימָתַי הָיָה זֶה. אִם בּוֹ בַּיּוֹם אוֹ לְמָחֳרָתוֹ"- עַגְנוֹן/ עִיר וּמְלוֹאָהּ, 112, וְכֵן: "בּוֹ בַּיּוֹם, לְאַחַר הַבְדָּלָה, הִמְצִיא עַצְמוֹ לִפְנֵי ר' בְּרִישֶׁל וְנִשְׁתַּעְשֵׁעַ עִמּוֹ בְּחִידּוּשֵׁי תּוֹרָה"- ח. הַז/ דּוֹרוֹת הָרִאשׁוֹנִים, 22)