釋氏要覽 2.332

2.332

欲有四種。一情。二色。三食。四婬欲。以希須為義。謂此界四欲具足。故名欲界。此有六天。謂。四王。忉利。夜摩。兜率。化樂。他化自在。

Desire is of four kinds: first, sentiment; second, form; third, food; fourth, sexual desire. It takes 'yearning and needing' as its meaning. It means this realm is fully endowed with these four desires; therefore, it is called the desire realm. Here there are six heavens, namely: the Four Heavenly Kings, Trāyastriṃśa, Yāma, Tuṣita, Nirmāṇarati, and Paranirmitavaśavartin.