What is a Phantonym?

What exactly is a phantonym? Well, it depends on whom you ask. If you ask Jack Rosenthal, a journalist and executive at The New York Times that coined the portmanteau word (phantom + antonym) in a column published on September 25, 2009, a phantonym is “a word that looks as if it means one thing but means quite another.” A perfect example is noisome. At first glance, it seems to be related to noise — something that is loud could be said to be noisome, right? Wrong — the word noisome is not related to noise at all (it is related the word annoy) and actually means having an extremely offensive smell. The secondary meaning of noisome is unpleasant or disagreeable.

Now if you ask Rod Evans, a professor of philosophy at Old Dominion University and author of five books on the English language, the definition of a phantonym is a bit different (and more closely related to antonym): 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.

Since phantonym has not made it into the Oxford English Dictionary, one can only assume that either definition is acceptable. Rosenthal’s definition favors the misleading quality of the word, so a better name would be a “misleading word” or a “deceptive word” rather than phantonym. On the other hand, Evans’s definition is more faithful to its second root word (antonym), focusing on the opposite meaning of specific word pairs. Regardless of which definition you favor, Rosenthal is absolutely correct when he advises “[a phantonym] warrants wariness.” Here are examples of phantonyms based on the two different definitions (definitions are used on primary usage, although modern usage has eclipsed the traditional, more proper meanings):

Rosenthal Phantonyms:
Arguably: it may  be argued, implying neutrality (the opposite of questionably is definitely)
Disinterested: unbiased or impartial (the opposite of interested is uninterested)
Enervated: weakened (the opposite of weakened is energized)
Enormity: an extreme wickedness (the opposite is smallness is immensity)
Fortuitous: occurring by chance (the opposite of unlucky is fortunate)
Fulsome: flattering excessively (the opposite of empty is full)
Noisome: having an extremely offensive smell (the opposite of quiet is noisy or noisiness)
Penultimate: second to the last (the opposite of worst or least is ultimate)
Presently: after a short time, soon (the opposite of past is present)
Restive: unable to keep still or quiet (the opposite of restless is restful)

Evans Phantonyms:
ahead – afoot
back up – back down
badly – goodly
breakdown – breakup
cargo – bus stop
catalog – dogwood
catwalk – dogtrot
coffee – coffer
downfall – uprise
enrage – outrage
famous – infamous
forgive – forget
founder – loser
giveaway – getaway
headlights – footlights
hereafter – therefore
inception – exception
inning – outing
intend – extend
layoff -standoff
left off – right on
maternity dress – paternity suit
offset – onset
outhouse – in-house
outgrown – ingrown
pair – impair
pale – impale
shut-out – shut-in
turndown – turn up
undergo – overcome
upright – downright
valuable – invaluable
walk-on – run off

Read related posts: What is the Longest Word in English Language?
Word Oddities: Fun with Vowels
What is an Abecedarian Insult?
Difficult Tongue Twisters
Rare Anatomy Words
What Rhymes with Orange?
Words with Letters in Alphabetical Order

For further reading: Tyrannosaurus Lex: The Marvelous Book of Palindromes, Anagrams, and Other Delightful and Outrageous Wordplay by Rod Evans (2012)
http://www.nytimes.com/2009/09/27/magazine/27FOB-onlanguage-t.html?_r=0