source ▁applications , ▁contains ▁the ▁following ▁longest ▁words , ▁which ▁are ▁ 4 0 ▁letters ▁long : ▁ ▁, ▁ ▁" car riers ' ▁li ability ▁ins urance "; ▁ ▁, ▁" dri vers ' ▁li ability ▁ins urance "; ▁ ▁, ▁" con form ity ▁assess ment ▁procedures " ▁( 3 8 ▁letters ) ▁ ▁The ▁word ▁often ▁said ▁to ▁be ▁the ▁longest ▁in ▁Dutch ▁– ▁probably ▁because ▁of ▁its ▁fun ny ▁meaning ▁and ▁all iter ation ▁– ▁which ▁has ▁also ▁appeared ▁in ▁print , ▁is ▁ ▁(" const ruction ▁ground ▁for ▁the ▁H ott ent ot ▁soldiers ' ▁t ents ▁exhibition "); ▁counting ▁ 5 3 ▁letters . ▁ ▁English ▁▁ ▁The ▁ 4 5 - letter ▁word ▁p neum on oul tr am icro scop ics il ic ov ol cano con ios is ▁is ▁the ▁longest ▁English ▁word ▁that ▁appears ▁in ▁a ▁major ▁dictionary . ▁ ▁Origin ally ▁co ined ▁to ▁become ▁a ▁candidate ▁for ▁the ▁longest ▁word ▁in ▁English , ▁the ▁term ▁eventually ▁developed ▁some ▁independent ▁use ▁in ▁medicine . ▁ ▁It ▁is ▁referred ▁to ▁as ▁" P 4 5 " ▁by ▁research ers . ▁ ▁Ant id is est ab lish ment arian ism , ▁at ▁ 2 8 ▁letters , ▁is ▁the ▁longest ▁non - co ined , ▁non - system atic ▁English ▁word ▁in ▁ ▁Oxford ▁D iction aries . ▁It ▁refers ▁to ▁a ▁ 1 9 th - century ▁political ▁movement ▁that ▁opposed ▁the ▁dis est ab lish ment ▁of ▁the ▁Church ▁of ▁England