The Longest Words in English
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.
45 Letters
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.
189,819 Letters
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.
28, 29, and 34 Letters
There are some long words that are rarely or never used in a sentence, but instead are simply used as examples of long words. 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.
49 Letters
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.
85 Letters
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. 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
30 Letters
Pseudopseudohypoparathyroidism, another medical term, refers to a relatively mild form of pseudohypoparathyroidism (helpful).
29 Letters
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.
23, 24, 25, 26, and 27 Letters
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.
Hydrochlorofluorocarbon (23 letters) refers to a type of gas also helpfully known as HCFC.
22 Letters
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.
21 Letters
Incomprehensibilities refers to things that are hard to comprehend or understand. (We’re pretty sure most of these words qualify.)
Pseudohermaphroditism refers to the condition of having the gonads and karyotype of one sex and external genitalia that is of the other sex or is ambiguous.
And finally, psychoneuroimmunology refers to a branch of medicine that deals with the influence of emotional states and nervous system activities on immune function.
Merriam Webster