Jiyun (Collection of Rhymes) and Yunhui (Collection of Rhymes) state it is pronounced fen. Jiyun defines it as the appearance of a towering mountain or hill. In the Zhuangzi, Chapter: Knowledge Wanders North (Zhuangzi: Zhi bei you), it is written: Ascending the towering Yin-fen hill. Furthermore, Guangyun (Broad Rhymes) and Jiyun (Collection of Rhymes) state it is pronounced fen (rising tone). The meaning is the same.