Nandaka (Sanskrit: नन्दक, lit. 'source of joy')[1] or Nandaki is the sword of the Hindu god Vishnu. Nandaka is generally depicted in images where Vishnu is represented with more than his usual four arms. The sword is compared to knowledge in Hindu scriptures.
In Sri Vaishnavism (a major Vaishnava tradition), the saints Annamacharya and Peyalvar are considered to be the avatars of Nandaka.