יָסַד (b. h.; v. סַד) [to join, fasten; denom. יְסוֹד, whence יָסַד] to found, establish. Tanḥ. B’resh. 1 ובה … וי׳ ארץ and with it (the Torah) he stretched the heavens and established the earth. Meg. 3ᵃ; Sabb. 104ᵃ; Succ. 44ᵃ וחזרו וִיסָדוּם and they reintroduced them. Ib. 20ᵃ, v. עֶזְרָא; a. fr.
Pi. - יִסֵּד, יִיסֵּד 1) to establish; to join in between. Y. Erub. V, 22ᶜ שער היסוד ששם היו מְיַיסְּדִין וכ׳ the Eastern Gate was named the Foundation Gate, because there they (in their meetings) established the decisions of the Law; a. e.—Part. pass. מְיוּסָּד. Ib. שער התווך שהוא מי׳ בין וכ׳ it was named the Middle Gate because it was fastened in between two gates; a. e. —2) to rebuild (a ruin). Tosef. B. Mets. XI, 4 לא יאמר לו הריני מייסד עמך מכנגד וכ׳ (not עמו) he has no right to say, I will help thee rebuild the party wall from where my (higher situated) ground commences and upward, אלא מייסד עמו וכ׳ but he must help him build from the bottom (of the neighbor’s ground) &c.; Y. ib. X, beg. 12ᶜ; (B. Bath. 6ᵇ מסייע מלמטה). [Cant. R. to I, 2 שהרי חבירו בא ליַסֵּד עליו כן the next following sentence comes to found upon it a base (thus proving that the reading is דּוֹדֶיךָ and not דּוֹדַיִךְ). Some eds. read לימד; Ab. Zar. II, 5 חבירו מלמד; Yalk. Cant. 981 מוכיח.]
Nithpa. - נִתְיַסֵּד to be established. Tanḥ. l. c. העולם לא נ׳ וכ׳ the world has been founded on nothing but the Law.