The longest word in Russian has 55 letters

The record holding word for the number of letters in Russian is: 'тетрагидропиранилциклопентилтетрагидропиридопиридиновые' (55 letters). It’s a chemical term denoting a class of organic compounds. 

In colloquial speech, long words are also frequent: ‘одиннадцатиклассница’ (‘11th-grader’ – 20 letters), ‘достопримечательность’ (‘landmark’ – 21 letters), ‘переосвидетельствование’ (‘re-evaluation’ – 23 letters).