wimlach wrote:
'The Umber' would be good if the river is described as often murky or muddy - perhaps the polite name is 'The Umber' while the local less flattering term for the river would be 'The Brown' or 'The Murk'.
It's appropriate as the 'real world' equivalent, 'The Thames', is derived from 'dark'.
'Umbra' in Latin means 'shadow' in English (I think), so it is a short leap to 'Umber'. As Wimlach says, the Thames is named after the old Celtic word for 'dark water', so if you want to maintain the creative link between Ellesland and the British Isles and you didn't want a Selentine influence in your naming convention, the Gaelic word for 'dark' is 'dorcha' and for 'shadow' is 'dubhar', so anything that plays around with those words could work (the Durk, the Dubar, the Orka, for example). But, for me, given the proximity of the Umber Downs, the Latin-rooted 'Umber' would get my vote.
If you're interested in translators to come up with your own inspiring words for your own place names, I can recommend Google's English to Irish translator:
https://translate.google.com/?hl=en#en/gaAnd for Scottish Gaelic, I can recommend:
https://glosbe.com/en/gdBut the British Isles is abound with old languages, like Cornish, Welsh, Manx, etc., so take your pick and off you go
. The provenance of a place name can also inspire some local history, too - for example, why did the Selentines rename the river to the Umber when they conquered Albion? Was it because they could not speak the native name, or did the native name mean something offensive to the Selentines, or was it just a show of authority? Are their cults that even now conspire to undo the Selentine influence and restore Albion's largest river's original name...?
The possibilities are endless. And that's without even considering whether the Otherworld has plans of its own for the river...