Arabic
A lot of people people believe that the word "Faasqanamokomoh" فأسقيناكموه (which means "we gave to you to drink) is the longest word in the Arabic language. That is not true at all. This word is the longest word in the holy Quran but not the longest in the whole Arabic language. For example take the word "A'Faasqanamokomoh" أفأسقيناكموه (Didn't we gave it to you to drink), this word is one litter longer than the previous one. A longer word is "A'faastasqinamokomoia" أفإستسقيناكموها which is 15 letters long.
Read more about this topic: Longest Words