Sammanasya Suktam is a hymn for unity or like-mindedness of the people. It is found in the Atharva Veda Samhita. It is called so because the deity or subject matter is sammanasyam, which means unit of mind or like-mindedness.
Sammanasya Suktam is used to promote agreement or unanimity in an assembly or in the society. Sammanasya Suktam of Rig Veda (with a few variants) is taken in Atharva Veda as Sammanasya Suktam (Atharva Veda VI – 64). Both have the same purport and thus underline the significance of unity of thought for some common cause. It describes how people should behave with each other to secure love and concord.
The hymn comprises seven mantras and prays for like-heartedness, like-mindedness, non-hostility and affection of one towards the others, like cow and her new born calf. For harmony in a family, the hymn states, a son should be loyal to his father and be of one mind with his mother. A wife should be calm, gentle and soft spoken. Brothers should not hate each other and sisters should not be unkind to each other. All family members should speak well of each other.
For concord and agreement in a group or assembly, like-mindedness is regarded as most essential. Joint labor, sharing of food and drinking together enhance the feeling of unity among people of different attitudes. The Vedic concept of Sammanasyam is the basis of corporate living for any community.
Source - Encyclopedia of Hinduism Volume IX - IHRF