A word so powerful it destroys prefixes

A word so powerful it destroys prefixes

My word for the day isn't terribly obscure, but it is quite curious. We all understand the prefix un to make a word its opposite. Married vs. unmarried. Appealing vs. unappealing. But the word ravel is so powerful that it destroys even this mighty prefix. Yes, folks, the words ravel and unravel mean virtually the same thing!