From Hull AWE
The noun phantonym may occasionally be seen in writings about English usage. AWE advises against it, as at least four different meanings have been proposed.
A phantonym may be:
- "a word that looks as if it means one thing but means quite another" (perhaps the most common current meaning). This was proposed by a journalist, Jack Rosenthal, in The New York Times in a column on September 25, 2009 ([]). The on-line Collins English Dictionary (14-04-16) reports that "We can't find much evidence of this word in actual use", and it has not yet (2016) been accepted into OED, but it is not hard to find on line. This meaning is close to those of false friend and malapropism, which may offer you a better word for your purpose.
- "a word or phrase that appears to be opposite in meaning to another word or phrase but isn’t. For example, inflammable seems to be the opposite of flammable (like inattentive vs. attentive). However inflammable is related to the word inflame, therefore inflammable actually means the ability to readily catch on fire". This meaning of phantonym was proposed by Rod Evans, a professor of philosophy at Old Dominion University and writer on the English language (information from []).
- In 2006 phantonym was used by Kit Whitfield to describe: "… the feeling you get when you're searching for the perfect word: that there is a word for this concept that's not in the thesaurus, but you can't quite remember it … and you're forced to go with a word that's slightly wrong" (information from []).
- Before then, in 1993, Irwin M. Berent used phantonym in the subtitle of Getting your Word's Worth as a clever blend of phantom and antonym, in relation to a discussion of antonyms (opposites) which didn't really exist but were made up for fun, such as understand/overstand and belittle/bebig. (information from []).
Because of this ambiguity, you are advised not to use phantonym.