A Hebrew verb meaning to be one, to join, to unite, or to act in unison. The related noun yachad (together, in unity) is among the most used Hebrew words in the Psalms. The concept underlies the Shema's declaration of divine oneness and the priestly prayer for unified worship.
Yachad and its derivatives carry the weight of covenantal unity — the kind of oneness that reflects the divine nature. Psalm 133 famously begins "How good and pleasant it is when God's people live together in unity (yachad)!" — describing it as anointing oil and refreshing dew. The Shema — "The LORD our God, the LORD is one (echad)" — implies a unity so profound that all of Israel's worship must be directed to this one God alone. Jesus prayed that His disciples would be one as He and the Father are one (John 17:22), making divine unity the template for human community.