Sîr Angren was the older, Sindarin name for the river better known by the name the Rohirrim gave it - the Isen.
angren in Sindarin, like Isen means "iron (adj)". Sîr Angren means "iron river".
Compare S. Angrenost and R. Isengard, both meaning Iron fortress.
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Unfinished Tales, "Aldarion and Erendis: The Mariner's Wife", note 6