The affix matup is added denoting a river.,
When the name of a river is to be designated by something which is found near it, we add the affix मतुप् (मत् and वत्). Thus उदुम्बरा꣡वती, मशका꣡वती, वीरणा꣡वती, पुष्करा꣡वती, इक्षु꣡मती, द्रु꣡मती ॥ See 6.3.119 by which the अ is lengthened in these words, and 6.1.219 by which the udatta is placed on this vowel. See 8.2.10 by which मत् becomes वत् ॥
The affix मतुप् is not however employed in forming the river-names भागीरथी and भैमरथी, which are formed by अण् added under 4.2.68.,