The Corieltauvi lived in the region of Leicester, Nottingham and Lincoln. The area is a low-lying one with many rivers: Ancholme, Brant, Devon, Eau, Erewash, Eye, Fleet, Greet, Idle, Langworth, Leen, Maun, Meden, North Beck, Poulter, Ryton, Slea, Smite, Soar, Till, Whipling, Witham, Wreak. Most important is the Trent which flows through the heart of the region and has many tributaries through the Lincolnshire fenlands.
Corieltauvi seems to be made up of three elements. The first can be taken as British corio- “host, army”, represented by the Middle Welsh cordd, “tribe, clan multitude, host”, Middle Irish cuire, “band, army”, and the the Gaulish tribal names Tricorii, “three hosts”, and Petrucorii, “four hosts”.
The second element –el- seems to correspond to Welsh el-, “many”, and related to the Old Irish il, “many, varied”. The Welsh el– is an archaism, suriving only in personal names as Elfed, Elgi and Elno. But the Irish il is very common in topographical formations. Significant in this context are il-adbai, “many dwellings”, il-chathraig, “many cities”, il-chricha, “many territories”, and il-uisci, “many waters”.
The last element –tauvi, can be related to the British or Pictish Tava or Tavus, the River Tay in Scotland. Tatha, the Gaelic name of the Tay, implies an original Tauia, with semi-vocalic u and i.
There are grounds, then, to take our British tribal name as Corieltavi, with the defiant meaning “army of (the land of) many rivers”, or “host of (the region of) many rivers.”
Andrew Breeze (2002). “Does Corieltavi Mean ‘Army of Many Rivers’?”. The Antiquaries Journal 82.