seder UK /ˈseɪdə/US /ˈseɪdɚ/ noun3 •(Judaism) The ceremonial meal held on the first night or first two nights of Passover. •(Judaism) A ceremonial meal held on Tu BiShvat, consisting of several types of fruits and nuts. •(Judaism) One of the 6 parts into which the Mishnah is divided. formssedarim · seders · sidarim · siddarim