such a grandiose name

Yes, David, it is a goody.

I reckon (without any evidence) that the derivation is from d'entre = "from between" and sangle = "strap, saddle, girth"
So Dentressangle = "from between (the) saddle(s)"

This doesn't make much sense at first glance, but in English we talk about the saddle of a hill, so perhaps it's a geographical reference?

Have to ask Norbert if his ancestors were born in the French equivalent of "The Valleys" for instance.

Are you around belM ? Does this look plausible to a French speaker?