I forgot to rename an item when I enchanted it. Is there any way I can rename it?
Sadly, no -- the enchanting process is the only time you can provide a custom name for any item. This is actually why I do so little of it -- I spend way too much time sitting at that screen trying to come up with a name that I won't despise an hour later, such as when I thought I was getting clever creating a ring of waterbreathing and naming it "Ring of the Fish"...
If you have a save from before you created the item, you can load that, enchant it again, and name it this time around. Or, you can create a new copy of the same item and then sell the original unnamed one (for a not-insignificant amount of gold, plus more enchanting experience!).