What is the meaning of the longest word in the English language which dictionaries have the space to include?

Question

"A Dictionary of the English Language", first published in 1755, becoming one of the most influential dictionaries in the history of the English language, was by whom?

Answer 1

Lung disease caused by the inhalation of silica or quartz dust
The word is "pneumonoultramicroscopicsilicovolcanoconiosis" (forty-five letters). Estimation of something as valueless is "floccinaucinihilipilification" (twenty-nine letters); the opposition etc is "antidisestablishmentarianism" (twenty-eight letters); things impossible to understand is "incomprehensibilities" (twenty-one letters) which was in the 1990s seen as the longest word in common usage. Two words not included in major dictionaries, presumably for lack of space, are the chemical terms "Methionylglutaminylarginyltyrosylglutamyl...serine) (1,809 letters) and "Methionylthreonylthreonylglutaminylalanyl...isoleucine " (189,819 letters); they are seen as the longest.