What’s the opposite of disgruntled? Chances are you’re thinking the answer should rightly be gruntled—but is that really a word you recognize? The problem here is that disgruntled, alongside the likes of uncouth, disheveled, distraught, inert, and intrepid, is an example of an unpaired word, namely one that looks like it should have an apparently straightforward opposite, but in practice really doesn’t.

Words like these tend to come about either when a prefixed or suffixed form of a word is adopted into the language while its root is not, or when the inflected or affixed form of a word survives, while its uninflected root form falls out of use. This was the case with disgruntled, which derives from an ancient Middle English word, gruntel, meaning “to grumble” or “complain,” which has long since fallen from use—although the gap left by disgruntled has led some dictionaries to list gruntled as a modern-day back-formation.

Some words and phrases, however, do have clear opposite forms, but they’re so rare or unfamiliar that they tend to remain forgotten. Eleven examples of precisely that are listed here.

1. AMBIDEXTROUS

If you’re ambidextrous then you’re equally skillful in using both hands (although perhaps not as successfully as President James Garfield). If you’re ambilevous however you’re equally clumsy using either hand—or, as Noah Webster defined it, “left handed on both sides.”

2. ANONYMOUS

Anonymous literally means “without a name.” Its opposite is onymous, which is typically used to refer to books, legal papers, artworks, musical compositions, and similar documents the authorship of which is known without doubt.

3. AUTOMATON

If an automaton is a machine capable of moving itself, then the opposite is called a heteromaton—a device that relies solely on external forces for movement.

4. CATASTROPHE

If a catastrophe is a sudden, unpredictable, and devastating event, then an equally sudden or unexpected event of sheer joy or good fortune is a eucatastrophe. This term was coined by Lord of the Rings author JRR Tolkien in 1944, who originally used it to describe a sudden or fortuitous event in the plot of a story that turns around the protagonist’s chances or prospects, and brings about the resolution of the narrative. 

5. DÉJÀ VU

Over the years, psychologists have identified a number of different phenomena similar to déjà vu (literally “already seen” in French). Among them is presque vu (“almost seen”), the tip-of-the-tongue feeling that you’re about to remember something you’ve forgotten; déjà vécu (“already experienced”), a particularly intense form of déjà vu that makes it almost impossible to discern the present from the past; and déjà visité (“already visited”), which describes a person’s surprising foreknowledge of a place they’ve never actually been to before—like unthinkingly knowing your way around a foreign town or city while on holiday. The opposite of déjà vu, however, is usually said to be jamais vu (“never seen”): so if déjà vu describes the eerie sensation that something new has actually taken place before, in the case of jamais vu a person believes that a situation that is actually very familiar and has happened before is entirely new.

6. DISTRESS

If you’ve been through a difficult or disturbing situation that left you upset or shaken up, then you’ve suffered distress. If you’ve been through a difficult or stressful situation that left you energized and compelled you to work or act better than you might otherwise do, then you’ve experienced eustress.

7. EUPHEMISM

If a euphemism involves the use of a politer word or phrase in place of a more distasteful or objectionable one, a dysphemism is the deliberate use of an impolite or unpleasant term in place of a perfectly inoffensive one. Dysphemism is often used for rhetorical effect, in order to shock or shake up an audience, or simply for comic effect.

8. OPTIMUM

Just as optimist is opposed to pessimist, optimum is the opposite of pessimum. So while the optimum conditions are those that are most favorable and suitable for doing something, the pessimum would be the worst or least favorable conditions.  

9. PLACEBO

Placebo literally means “I shall please” in Latin, and the placebo effect refers to an apparent improvement or amelioration in a patient’s condition despite them deliberately being given entirely ineffectual “dummy” medication. The opposite phenomenon is called the nocebo effect, which describes a patient reporting that they feel worse despite being given an entirely harmless treatment; it might sound like a made-up name, but nocebo actually means “I shall harm” in Latin.

10. POSTPONE

To bring a date forward in time rather than postponing it is to prepone it.

11. STOCKHOLM SYNDROME

Taking its name from a hostage situation that unfolded after a bank robbery in Sweden in 1973, Stockholm syndrome refers to the psychological phenomenon of hostages becoming sympathetic towards their captors. An opposite phenomenon is called Lima syndrome, in which it is the hostage-takers who gain sympathy for their hostages. And just like Stockholm syndrome, Lima syndrome too has its roots in a real-life hostage situation that occurred after a local militia stormed a party being held at the Japanese Embassy in the Peruvian capital in 1996.

Is it true that if you wear a hat often enough it will cause you to bald? In short: No. Whether or not you keep your hair is up to genetics. Allow mental_floss List Show host Craig Benzine to walk you through the common causes of baldness and debunk this myth once and for all.