What is the longest word in the English dictionary? Plus 14 other words with lots of letters

In English speaking countries, there are millions of words that people can choose from to express themselves - all helpfully written down in dictionaries for reference. Some words are used regularly without much thought, such as ‘like’ or ‘you’, but others are a bit more mind-boggling. Some, for example, are notable because of their impressive length.

There is some disagreement about what the longest word in English is. Some people believe it is the name of a compound, abbreviated as ‘methionylthreonylthreonylglutaminylalanyl…isoleucine’. It’s impossible for us to write the full length of this word as it’s actually 189,819 letters long! It allegedly takes around three hours to say and is the chemical name for the largest known protein, titin. There are people who do not believe this counts, however, as it is not a word that would ever be used in everyday life, and as such it’s not included in any dictionary - so we haven’t included it in this list.

Below, you’ll find a list of the longest words you will find in the English language. Some of them are more obscure than others, and some will be used more regularly than others also, but you’ll find them all in the pages of your dictionary. If you like to use particularly long words then you are a sesquipedalian - and, in a fun twist, that happens to be another pretty long word.  

Keep reading to find out the longest word in the dictionary, plus 14 others. If you fancy challenging yourself, see how many you can pronounce too. To learn even more about language, take a look at our dedicated words and meanings page which includes articles such as 35 untranslatable words from around the world, along with commonly used oxymorons and 14 portmanteaus words and their meanings.

Pneumonoultramicroscopicsilicovolcanoconiosis

This word has an incredible 45 letters, and is the longest word written in most standard English dictionaries. If you’ve never heard it before, that’s probably because it’s a lung disease caused by inhalation of very fine silicate or quartz dust - so not something you’ll hear much about. Medically, it’s the same as silicosis, and that word is much easier to say.

Supercalifragilisticexpialidocious

This word has 34 letters. It might cause some controversy by being on this list as there is some debate as to whether or not it’s a real word, given that it was made up for the Walt Disney film Mary Poppins. But it’s listed on Dictionary.com, and people widely understand it to mean something which is fun or exciting, so that’s good enough for us to include it on the list.

Pseudopseudohypoparathyroidism

This word has 30 letters. This is another word with links to the health industry and refers to is an inherited condition that causes short stature, round face, and short hand bones. It’s also called Albright's Hereditary Osteodystrophy which is much easier to pronounce.

Flocci­nauci­nihili­pili­fication

This word has 29 letters. It combines four Latin words that mean "nothing" and the word itself is defined as "the act of estimating something as worthless". It was used commonly during the 18th century, but isn’t used as much today.

Antidisestablishmentarianism

This word has 28 letters and refers to the opposition of the disestablishment of the Church of England. It’s not used much in the 21st century, but it was used a lot in the 19th century.

Honorificabilitudinitatibus

This word has 27 letters and means the state of being able to achieve honours. As well as being one of the longest words in the English dictionary, it’s also the longest word used by Shakespeare in his works. It is mentioned by the character Costard in Love's Labour's Lost.

Electroencephalographically 

This is another word which also has 27 letters. It’s a device used for recording the electrical activity of the brain, usually by placing electrodes on someone’s scalp. This method is used to diagnose tumours of the brain and to study brain waves. It’s shortened in the medical industry to EEG.

Laryngotracheobronchitis

This word has 24 letters. As the name suggests, it refers to inflammation of the larynx, trachea, and bronchi. It affects the lower airway which means it can be more severe than laryngotracheitis.

Deinstitutionalisation 

This word has 22 letters. It refers to the movement during the 1950s where patients in mental health asylums, such as psychiatric hospitals, were relocated to live with their families or in community-based homes.

Counterrevolutionaries

This is another word with 22 letters. A counter revolution is a revolution directed toward overthrowing a government or social system which had been created by a previous revolution. A counterrevolutionary is someone who carries this out.

Incomprehensibilities

This word has 21 letters. It’s one of the longest words that is in everyday use in the English language and refers to things which are difficult to comprehend and understand.

Uncharacteristically

This word has 20 letters, and is another longer word which you are more likely to use everyday. It is defined as things which are not typically associated with a thing or a person.

Indistinguishability

This is another word which has 20 letters and could be used in common conversations. It means things which are so similar it is not possible to see differences between them.

Keratoconjunctivitis

This is another word with links to health, and has a total of 20 letters. It is an eye condition that involves inflammation of both the cornea and conjunctiva at the same time.

Paleoanthropological

This word also has 20 letters. A paleoanthropological study is one which seeks to understand the early development of anatomy of modern humans through the study of kinship lines, biological evidence and cultural evidence.