The Longest Long Words List

Most English words longer than about 15-20 letters are scientific, meaningless, or highly specialized, and they tend to be formed by affixation. This is the act or process of adding affixes to a base word to produce a derivative word—in the word affixation, for instance, -ation is an affix. Here are some of the longest words.

The longest word entered in most standard English dictionaries is Pneumonoultramicroscopicsilicovolcanoconiosis with 45 letters. Our definition is "a lung disease caused by inhalation of very fine silicate or quartz dust." The entry for this word can be found in our Medical Dictionary.

Yes, that number is correct. The longest string of letters used to describe something isn't technically a word—it's the chemical name for a protein, begins with methionylthreonylthreonylglutaminyl..., and continues for quite a while after that. The name has 189,819 letters, fills more than 50 pages, and takes more than three hours to say. If you've got three hours to blow, you can listen to it said here.

There are some long words that are rarely or never used in a sentence, but instead are simply used as examples of long words, and for that reason we don’t include them in our dictionaries. The most famous of these are antidisestablishmentarianism, which has 28 letters and supercalifragilisticexpialidocious, which has 34 letters. Floccinaucinihilipilification (29 letters) ("the act or habit of assessing something as worthless") is another of this ilk. Our claim is not that these aren’t words, but that they aren't words that meet our criteria for entry. We explain why here.

The longest place name in the United States is possibly a lake in Massachusetts called Lake Chargoggagoggmanchauggauggagoggchaubunagungamaugg (49 letters, or 53, if you count the Lake portion). It is also sometimes called Webster Lake. While the longer name is based on earlier names for the lake from the language of the Nipmuc people who inhabited the area, this version of the name—along with its reputed translation, "You fish on your side; I fish on my side; nobody fishes in the middle”—appears to have been the invention of a local newspaper editor.

The longest place name in the English-speaking world is thought to be a 1,001-foot-high hill in New Zealand called Taumatawhakatangihangakoauauotamateaturipukakapikimaungahoronukupokaiwhenu-akitanatahu. Similar to the lake mentioned above, this place name also has spelling variations. It comes from the Maori language and has been translated as “the place where Tamatea, the man who had big knees, the climber of mountains, the slider, the land-swallower that traveled about, played the nose flute that he had to the loved ones.” The hill is sometimes called “Taumata” for short.

Pseudopseudohypoparathyroidism, another medical term, refers to a relatively mild form of pseudohypoparathyroidism (helpful). This is the only word in our dictionary with a repeating pseudo.

Methylenedioxymethamphetamine refers to a synthetic amphetamine used illicitly for its mood-enhancing and hallucinogenic properties. You may know this drug by another, shorter, name: ecstasy. Or you may know it by an even shorter name: MDMA. (Fun fact: in the 1970's psychiatrists used it to "enhance" therapy sessions.)

You can look these up if you want to, but they're long and technical so we've only put brief definitions here.

If you do something electroencephalographically (27 letters) you do it using an apparatus for recording brain waves—that is, an electroencephalograph.

Radioimmunoelectrophoresis (26 letters) refers to a kind of immunoelectrophoresis involving radioactive labels.

If you do something immunoelectrophoretically (25 letters) you do it with immunoelectrophoresis, natch.

Laryngotracheobronchitis (24 letters) refers to inflammation of the larynx, trachea, and bronchi. (Yikes.)

Hydrochlorofluorocarbon (23 letters) refers to a type of gas also helpfully known as HCFC.

Counterrevolutionaries refers to people who participate in a revolution directed toward overthrowing a government or social system established by a previous revolution.

Deinstitutionalization refers to the release of institutionalized individuals from institutional care (as in a psychiatric hospital) to care in the community, and also to the reform or modification of an institution to remove or disguise its institutional character..

Otorhinolaryngological refers to a medical specialty concerned especially with the ear, nose, and throat and related parts of the head and neck.