Silicosis (also known as pneumonoultramicroscopicsilicovolcanoconiosis, previously miner's phthisis, grinder's asthma, potter's rot and other occupation-related names) is a form of occupational lung disease caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lungs. It is a type of pneumoconiosis.

Silicosis (particularly the acute form) is characterized by shortness of breath, cough, fever, and cyanosis (bluish skin). It may often be misdiagnosed as pulmonary edema (fluid in the lungs), pneumonia, or tuberculosis.

Silicosis resulted in 46,000 deaths globally in 2013 down from 55,000 deaths in 1990.

The name "silicosis" (from the Latin "silex", or flint) was originally used in 1870 by Achille Visconti (1836–1911), prosector in the Ospedale Maggiore of Milan. The recognition of respiratory problems from breathing in dust dates to ancient Greeks and Romans. Agricola, in the mid-16th century, wrote about lung problems from dust inhalation in miners. In 1713, Bernardino Ramazzini noted asthmatic symptoms and sand-like substances in the lungs of stone cutters. With industrialization, as opposed to hand tools, came increased production of dust. The pneumatic hammer drill was introduced in 1897 and sandblasting was introduced in about 1904, both significantly contributing to the increased prevalence of silicosis.

Pneumonoultramicroscopicsilicovolcanoconiosis () is a word invented by the president of the National Puzzlers' League as a synonym for the disease known as silicosis. It is the longest word in the English language published in a dictionary, the "Oxford English Dictionary", which defines it as "an artificial long word said to mean a lung disease caused by inhaling very fine ash and sand dust."

Silicosis is a form of occupational lung disease caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lungs. It is a type of pneumoconiosis.

Because chronic silicosis is slow to develop, signs and symptoms may not appear until years after exposure. Signs and symptoms include:

- Dyspnea (shortness of breath) exacerbated by exertion

- Cough, often persistent and sometimes severe

- Fatigue

- Tachypnea (rapid breathing) which is often labored,

- Loss of appetite and weight loss

- Chest pain

- Fever

- Gradual darkening of skin (blue skin)

- Gradual dark shallow rifts in nails eventually leading to cracks as protein fibers within nail beds are destroyed.

In advanced cases, the following may also occur:

- Cyanosis, pallor along upper parts of body (blue skin)

- Cor pulmonale (right ventricle heart disease)

- Respiratory insufficiency

Patients with silicosis are particularly susceptible to tuberculosis (TB) infection—known as silicotuberculosis. The reason for the increased risk—3 fold increased incidence—is not well understood. It is thought that silica damages pulmonary macrophages, inhibiting their ability to kill mycobacteria. Even workers with prolonged silica exposure, but without silicosis, are at a similarly increased risk for TB.

Pulmonary complications of silicosis also include Chronic Bronchitis and airflow limitation (indistinguishable from that caused by smoking), non-tuberculous Mycobacterium infection, fungal lung infection, compensatory emphysema, and pneumothorax. There are some data revealing an association between silicosis and certain autoimmune diseases, including nephritis, Scleroderma, and Systemic Lupus Erythematosus, especially in acute or accelerated silicosis.

In 1996, the International Agency for Research on Cancer (IARC) reviewed the medical data and classified crystalline silica as "carcinogenic to humans." The risk was best seen in cases with underlying silicosis, with relative risks for lung cancer of 2–4. Numerous subsequent studies have been published confirming this risk. In 2006, Pelucchi et al. concluded, "The silicosis-cancer association is now established, in agreement with other studies and meta-analysis."

Pneumoconiosis is an occupational lung disease and a restrictive lung disease caused by the inhalation of dust, often in mines and from agriculture.

In 2013, it resulted in 260,000 deaths, up from 251,000 deaths in 1990. Of these deaths, 46,000 were due to silicosis, 24,000 due to asbestosis and 25,000 due to coal workers pneumoconiosis.

In 2013 pneumoconiosis resulted in 260,000 deaths up from 251,000 deaths in 1990. Of these deaths 46,000 were due to silicosis, 24,000 due to asbestosis and 25,000 due to coal workers pneumoconiosis.

This word was invented at the annual meeting of the National Puzzlers' League (N.P.L.) by its president Everett M. Smith. The word featured in the headline for an article published by the "New York Herald Tribune" on February 23, 1935, titled "Puzzlers Open 103rd Session Here by Recognizing 45-Letter Word":

Subsequently, the word was used in a puzzle book, "Bedside Manna", after which time, members of the N.P.L. campaigned to include the word in major dictionaries.

This 45-letter word, referred to as "P45", first appeared in the 1939 supplement to the "Merriam-Webster New International Dictionary, Second Edition".