Phantonym

A phantonym is a word that appears to mean one thing, but in fact means another. 
The term was coined by Jack Rosenthal in his 2009 article for the NY Times. An example of phantonym usage noted in the article was when Barack Obama said, "I just want to make sure that we're having an honest debate and presenting to the American people a fulsome accounting of what is going on in this program," where he meant "full" instead of "fulsome". Phantonyms are usually .