一個英文單詞的組成不是幾個字母隨意合成的，是依照一定的規則建立起來的。網上流傳着世界上最長的英文單詞有189819個字母這個說法是不真實的。事實上世界上最長的單詞只有45個字母：pneumonoultramicroscopicsilicovolcanoconiosis，肺塵病，矽肺病，更準確來說是火山的灰塵引起的肺塵病，矽肺病。
像pneumonoultramicroscopicsilicovolcanoconiosis這種新的單詞是根據一些詞根建立的，它的詞根來源就有：pneumono- (of lung 肺的);ultra- (beyond 越過);micro (very small 極小的);scopic- (of viewing or observing 觀察或注意的);silico- (of silicon 硅的);volcano- (mountain that releases fire and ash 火山的);coni- ( koni， of dust 塵土的);osis-(forming the name of a disease 表示疾病)。像這樣創建單詞的還有地名，科技詞彙這些。這些類別的單詞通常也都會很長。
網絡上的誤傳，世界上最長的單詞有189819個字母的消息只是網絡上的謠言，稱含有267種種氨基酸的酶——肌聯蛋白它的化學名根據英文造字規則，一共有189819個字母，全部讀完需要花費約3.5小時。以下單詞有1909個字母，全部讀完需要花費約25分鐘，是它的一類：
MethionylglutaminylarginyltyrosylglutamylserylleucylphenylalanylalanylglutaminylleucyllysylglutamylarginyllysylglutamylglycylalanylphenylalanylvalylprolyphenylalanYlvalythreonylleucylglycylaspartylprolylglycylisoleucylglutamylglutaminylsErylleucyllysylisoleucylaspartylthreonylleucylIsoleucylglutamylalanylglycylalanylasparthlalanylleucylglutamylleucylglycylisoleucylprolylphenylalanylseRylaspartylprolylleucylalanylaspartylglycylpRolylthreOnylisoleucylglutaminylasPfraginylalanylthreonylleucylarfinylalanylphenylalanylalanylalanylglycylvalythreonylprolylalanylglutaminylcysteinylphenylalanylglutamylmethionylleucylalanylleuOylisoleucylarginylglutaminyllysyhistidylprolylthreonylisoleucylprolylisoleucylglycylleucylmethionyltyrosylalanylasparaginylleucylvalylphenylalanylasparaginyllysyglycylisoleucylaspartylglutamylphenylalanylthrosylalanylglutaminylcysteinylglutamyllysylvalylglycylvalylaspartylserylvalylleucylvalylalnylaspartylvalylprolylvalylglUtaminylglutamylserylalanylprolylphenylalanylarginylglutaminylalanylalanylleucylarginylhistidylasparaginyvalylalanylprolylisoleucylprolylisoleucylphenylalanylisoleucylphenylalanylisoleucylcysteinylprolylprolylaspartylalanylaspartylaspartylaspartylleucylleucylarginylglutaminylisoleucylalanylseryltyrosylglycylarginylglycyltyrosylthreonyltyrOsylleucylleucylserylarginylalanylglycylvalylthreonylglycylalanylglutamYlasparainylarginylalanylalanylleucylprolylleucylasparaginylhistidylleucylValylalanyllysylleucyllysylglutamyltyrosylasparaginylalanylalanylprolylprolylleucylglutaminylglgycylphenylalanylglycylisoleucylserylalanylprolylaspartylglutaminylvalyllysylalanylalanylisoleucylaspartylalanylglycylalanylalanylglycylalanylisoleucylserylglycylserylalanylisoleucylvalyllysylisoIeucylisoleucylglutamylglutaminylHistidylasparaginyliSoleucylglutamylprolylglutamyllysylmethionylleucylalanylalanylleucyllysylvalylphenylalanylcalylglutaminylprolylmethionlysylalanylalanylthreonylarginylserine 其實這個單詞只是所有氨基酸的英文名排列組合到一起，其真正只有5個字母Titin。
此外還有：Lopadotemachoselachogaleokranioleipsanodrimhypotrimmatosilphioparaomelitokatakechymenokichlepikossyphophattoperisteralektryonoptekephalliokigklopeleiolagoiosiraiobaphetraganopterygon這172個字母表示一種食物的單詞，可能和1909個字母的單詞一樣組合出來的。英語字典對這類詞打死都不會收錄的。
