There's been some debate over this issue and where exactly Oda drew inspiration from in terms of a name. But after covering Mesopotamian culture in History, I think I've got it.
The canon spelling is "Enel".
After going through several of the Sumerian Gods, here's what I've found relating to any part of his name:
Cheif God - Anu, the Sky God. Most worshipped, gives structure to the universe.
Forget the name and you pretty much have Enel in a nutshell. As for the name…
Next worshipped, Enlil, God of Wind and Air. Caused floodins and drought.
God of Wind and Air sounds plausible for Enel as well. Plus, the name is strikingly similar. Also notice how the Skypieans lived in fear of "God" and the things they said might anger him. This was prevalent in Sumerian culture by all means.
Scroll down to Enlil's section.