Learn English – term for what ‘sheveled’ is to ‘disheveled’

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Is there a term to describe an unprefixed term like sheveled that is used less or not at all compared to its prefixed relative disheveled?

My word Helen, you look very sheveled today!

Edit: Below Malvolio brings up the example of kempt which is another example of what I'm talking about. A word that has both prefixed and unprefixed forms in English, but the unprefixed form has mostly fallen out of use.

kempt vs. unkempt

Best Answer

This reminded me of Justice Scalia's telling off of a lawyer for using the word choate, which doesn't exist. According to the New York Times article, it's called back-formation:

Stripping the in- from inchoate is known as back-formation, the same process that has given us words like peeve (from peevish), surveil (from surveillance) and enthuse (from enthusiasm). There’s a long linguistic tradition of removing parts of words that look like prefixes and suffixes to come up with “roots” that weren’t there to begin with. Some back-formations work better than others.