一个英文单词的组成不是几个字母随意合成的，是依照一定的规则建立起来的。网上流传着世界上最长的英文单词有189819个字母这个说法是不真实的。事实上世界上最长的单词只有45个字母：pneumonoultramicroscopicsilicovolcanoconiosis，肺尘病，矽肺病，更准确来说是火山的灰尘引起的肺尘病，矽肺病。
像pneumonoultramicroscopicsilicovolcanoconiosis这种新的单词是根据一些词根建立的，它的词根来源就有：pneumono- (of lung 肺的);ultra- (beyond 越过);micro (very small 极小的);scopic- (of viewing or observing 观察或注意的);silico- (of silicon 硅的);volcano- (mountain that releases fire and ash 火山的);coni- ( koni， of dust 尘土的);osis-(forming the name of a disease 表示疾病)。像这样创建单词的还有地名，科技词汇这些。这些类别的单词通常也都会很长。
网络上的误传，世界上最长的单词有189819个字母的消息只是网络上的谣言，称含有267种种氨基酸的酶――肌联蛋白它的化学名根据英文造字规则，一共有189819个字母，全部读完需要花费约3.5小时。以下单词有1909个字母，全部读完需要花费约25分钟，是它的一类：
MethionylglutaminylarginyltyrosylglutamylserylleucylphenylalanylalanylglutaminylleucyllysylglutamylarginyllysylglutamylglycylalanylphenylalanylvalylprolyphenylalanYlvalythreonylleucylglycylaspartylprolylglycylisoleucylglutamylglutaminylsErylleucyllysylisoleucylaspartylthreonylleucylIsoleucylglutamylalanylglycylalanylasparthlalanylleucylglutamylleucylglycylisoleucylprolylphenylalanylseRylaspartylprolylleucylalanylaspartylglycylpRolylthreOnylisoleucylglutaminylasPfraginylalanylthreonylleucylarfinylalanylphenylalanylalanylalanylglycylvalythreonylprolylalanylglutaminylcysteinylphenylalanylglutamylmethionylleucylalanylleuOylisoleucylarginylglutaminyllysyhistidylprolylthreonylisoleucylprolylisoleucylglycylleucylmethionyltyrosylalanylasparaginylleucylvalylphenylalanylasparaginyllysyglycylisoleucylaspartylglutamylphenylalanylthrosylalanylglutaminylcysteinylglutamyllysylvalylglycylvalylaspartylserylvalylleucylvalylalnylaspartylvalylprolylvalylglUtaminylglutamylserylalanylprolylphenylalanylarginylglutaminylalanylalanylleucylarginylhistidylasparaginyvalylalanylprolylisoleucylprolylisoleucylphenylalanylisoleucylphenylalanylisoleucylcysteinylprolylprolylaspartylalanylaspartylaspartylaspartylleucylleucylarginylglutaminylisoleucylalanylseryltyrosylglycylarginylglycyltyrosylthreonyltyrOsylleucylleucylserylarginylalanylglycylvalylthreonylglycylalanylglutamYlaspaylarginylalanylalanylleucylprolylleucylasparaginylhistidylleucylValylalanyllysylleucyllysylglutamyltyrosylasparaginylalanylalanylprolylprolylleucylglutaminylglgycylphenylalanylglycylisoleucylserylalanylprolylaspartylglutaminylvalyllysylalanylalanylisoleucylaspartylalanylglycylalanylalanylglycylalanylisoleucylserylglycylserylalanylisoleucylvalyllysylisoIeucylisoleucylglutamylglutaminylHistidylasparaginyliSoleucylglutamylprolylglutamyllysylmethionylleucylalanylalanylleucyllysylvalylphenylalanylcalylglutaminylprolylmethionlysylalanylalanylthreonylarginylserine 其实这个单词只是所有氨基酸的英文名排列组合到一起，其真正只有5个字母Titin。
此外还有：Lopadotemachoselachogaleokranioleipsanodrimhypotrimmatosilphioparaomelitokatakechymenokichlepikossyphophattoperisteralektryonoptekephalliokigklopeleiolagoiosiraiobaphetraganopterygon这172个字母表示一种食物的单词，可能和1909个字母的单词一样组合出来的。英语字典对这类词打死都不会收录的。
