EIRUVIN Eiruvin are halakhic devices relating to Shabbat and Yom Tov by which the sages “joined” different domains of space and time. Eiruv comes from the same root as erev, “evening,” the time that joins day and night; arev, a “guarantor,” who joins another in a bond of shared responsibility; and arev, “pleasant,” the mood that prevails when people join in friendship. An Eiruv softens the sharp divides of boundaries.