Normally, when adding the letters "un" to the beginning of a word, it is a prefix that makes the word mean its opposite. For example, "clean" and "unclean", "lock" and "unlock", and "friendly" and "unfriendly".
Then I noticed the words "canny" and "uncanny". Not only is uncanny not its opposite, but it means even more so! So, I've been asking people for words that when the letters "un" are attached to its beginning, that the word does not mean its opposite. An early candidate mentioned by my brother was "icicle" and "unicycle". That sounded great, until we realized the spelling difference. A friend mentioned "it" and "unit", which I particularly liked. I wanted to add "animus" and "unanimous", but my lexicon shattered those dreams.
So far the list is:
Added: less/unless (Twirlip)
Added: to/unto (Friend)
Added: ionize/unionize (Dannon)