By Swami Harshananda
sāmnāyya (‘to put together’)
It is a mixture of freshly boiled milk mixed with sour milk or curds of the preceding night’s milking, offered as oblation to Indra (or Mahendra) in sacrifices like the Darśa, by one who has performed Somayāga.
Some authorities allow its offering even to those who have not performed the Somayāga.
- The Concise Encyclopedia of Hinduism, Swami Harshananda, Ram Krishna Math, Bangalore