Many negative words beginning with in- and some with im- do not become positive words by simply dropping the negative prefix -e.g., perious is not a word. I found no un-words of interest.
Quiz: Pick which of the words in this list are not words with the prefix removed.
Word Ways: Vol. 53
, Article 15.
Retrieved from: https://digitalcommons.butler.edu/wordways/vol53/iss4/15