https://www.mentalfloss.com/article/49720/12-lonely-negative-words
From "Mental Floss" - Are you disgusted, disgruntled and disheveled? Well, unfortunately you’re never going to be gusted, gruntled or sheveled.
Disgusted, disgruntled and
disheveled are what you might call “lonely negatives.” They’re negative words whose positive partners have vanished or never existed in the first place.
I have been whelmed, kempt and plussed before... in addition to having been underwhelmed, overwhelmed, unkempt and nonplussed.