יִסּוּד, (יָסַד) institution, confirmation; reestablishment. Men. 99ᵃ sq., v. בִּיטּוּל. Succ. 44ᵃ ערבה י׳ נביאים the use of the willow-branch (on Hoshanah Rabbah) is an institution of the prophets, opp. מנהג נביאים a custom arisen in the days of the prophets; Y. Shebi. I, 33ᵇ bot. מִיִּ׳ נביאים וכ׳ belong to the institutions of the early prophets; Y. Succ. IV, beg. 54ᵇ