Shiva Purana
यस्मात्सोमो महादेवो नन्दी चानेन नन्दितः ॥ सोमनन्दीति विख्यातस्तस्मादेष समाख्यया ॥ ३५ ॥
He was named Somanandin because Soma means Śiva and this tiger pleased Soma as well as Nandin.
english translation
yasmAtsomo mahAdevo nandI cAnena nanditaH ॥ somanandIti vikhyAtastasmAdeSa samAkhyayA ॥ 35 ॥
hk transliteration by Sanscript