法華義疏 1.370

1.370

「難陀」此云歡喜。「跋難陀」此云賢歡喜。此二龍王是兄弟，常令風不搖條、雨不破塊，見者歡喜故云歡喜。又是王舍城舊住，故初列之。

“Nanda” translates here as “Joy.” “Upananda” translates here as “Virtuous Joy.” These two dragon kings are brothers. They constantly cause the wind not to shake the twigs and the rain not to break the clods of earth; those who see them rejoice, hence they are called “Joy.” Furthermore, they were longtime dwellers in Rājagṛha, so they are listed first.