Etymology of Lille
The river "Deule" embraced the city of Lille. The city was a kind of island. In the early days, people spoke of "Isla" or "insula" in Latin. Literally the island, in French "Isle". This evolved into "Lille". In Dutch an analogous development: 'isla' to 'Lissele', to 'Rissele' to 'Rijsel'.
Bart Van Loo (2024) 
Gnostotheca 9076