Knowledge acquired in childhood (which is well-remembred/ to learn (something) with one's mother's milk
Fundamental learning that a person acquires in childhood. Learning that is well preserved in memory according to the idea expressed in Avot de-Rabbi Natan, chapter 4: "One who learns Torah in his youth, the words of Torah are absorbed with his very marrow" (literally: learning of childhood).
(“And that completes it! – What emerges from it is the version of youth.” — Shabbat 21b.And likewise: “The version of youth endures more than that of old age.” — Rashi, Shabbat 21b.And likewise: “Woe, woe to the tongue of one who forgot the version of youth.” — Mendelai, bookseller / in the yeshiva of Ma’alah.And likewise: “In order to remind himself of the version of youth, he asked me about it two and a half years ago, at the hour of the early study session.” — Agnon, Al Kapot HaManul, In Our Youth and in Our Old Age, p. 222.)
Translation
Expression (Hebrew)
גִּרְסָא דְּיַנְקוּתָא
Definition (Hebrew)
לִמּוּד בְּסִיסִי שֶׁלָּמַד אָדָם בְּיַלְדוּתוֹ. לִמּוּד שֶׁנִּשְׁמַר הֵיטֵב בַּזִּכָּרוֹן ע"פ הָרַעֲיוֹן הַמּוּבָא בְּאָבוֹת דְּרַבִּי נָתָן כַּד ד:"הַלּוֹמֵד תּוֹרָה בְּיַלְדוּתוֹ דִּבְרֵי תּוֹרָה נִבְלָעֵן בְּדִמְיוֹ" (מִלּוּלִית: לִמּוּד שֶׁל הַיַּלְדוּת).
("וְהָא גָּמְרָה!- נָפְקָא מִנַּהּ לְגִרְסָא דְיַנְקוּתָא"- שַׁבָּת כא ע"ב, וְכֵן:"גִּרְסָא דְּיַנְקוּתָא- מִתְקַיֵּם יוֹתֵר מִשֶּׁל זִקְנָה"- רָשִׁ"י מַסֶּכֶת שַׁבָּת כא ע"ב, וְכֵן:"וִי וִי לָבָן פֶּיְבּוּשׁ שֶׁשָּׁכַח גִּרְסָא דְּיַנְקוּתָא"- מֶנְדֵּלֵי מוֹכֵר סְפָרִים/ בִּישִׁיבָה שֶׁל מַעְלָה, וְכֵן:"כְּדֵי לְהַזְכִּיר לְעַצְמוֹ גִּרְסָא דְּיַנְקוּתָא שָׁאַל מִמֶּנִּי לִפְנֵי שְׁתֵּי שָׁנִים וּמֶחֱצָה שְׁתֵּי חוֹבֶרֶת שֶׁל הַשַּׁחַר"- עַגְנוֹן/ עַל כַּפּוֹת הַמַּנְעוּל, בִּנְעָרֵינוּ וּבִזְקֵנֵינוּ, 222)