Rasa (rásā रसा) is the name of a western tributary of the Indus in the Rigveda (verse 5.53.9). The word rasa means "moisture, humidity" in Vedic Sanskrit. In RV 9.41.6, RV 10.108 and in the Nirukta of Yaska, it is the name of a mythical stream supposed to flow round the earth and the atmosphere (compare Oceanus), also referring to the underworld in the Mahabharata and the Puranas (compare Styx). The corresponding term in Avestan is Ranha/Raŋhā. In the Vendidad, Ranha is mentioned just after Hapta-Həṇdu, and may possibly refer to the ocean.