The longest scientific term in English is the full chemical name of the world's largest known protein, titin. Beginning with Methionyl... and ending with ...isoleucine, the word contains 189,819 letters.
The 45 letter word “ Pneumonoultramicros copicsilico volcanoconiosis” is the longest English word that appears in a major dictionary. Originally coined to become a candidate for the longest word in English, the term eventually developed some independent use in medicine. It is referred to as "P45" by researchers.
“Antidisestablishmen tarianism” , at 28 letters, is the longest non-coined, non-technical English word. It refers to a 19th century political movement that opposed the disestablishment of the Church of England as the state church of England.
“ Floccinaucinihilipi lification” at 29 letters (and meaning the act of estimating something as being worth so little as to be practically valueless, or the habit of doing so) is the longest non-technical, coined word in the English language.
“ Hippopotomonstroses quipedaliop hobia” – fear of long words, at 35 letters could also be considered the longest non-coined, non-technical word. Although it is a "phobia" so is often seen as "technical". Hippopoto- "big" due to its allusion to the Greek-derived word hippopotamus (though this is derived as hippo- "horse" compounded with potam-os "river", so originally meaning "river horse"; according to the Oxford English, "hippopotamine" has been construed as large since 1847, so this coinage is reasonable); -monstr- is from Latin words meaning "monstrous", -o- is a noun-compounding vowel; -sesquipedali- comes from "sesquipedalian" meaning a long word (literally "a foot and a half long" in Latin), -o- is a noun-compounding vowel, and -phobia means "fear".
The longest word in Bulgarian is ?????????????????????????????? ????????? (Ne protivokonstitutsio nstvuvatels tvuvate), which are 39 letters and means "Do not act against the Constitution. "