What is the longest word in the Chambers Dictionary?

PNEUMONO­ULTRA­MICRO­SCOPIC­SILICO­VOLCANO­CONiOSIS is the longest Word in the Chambers, Webster's and Random House dictionaries. It is seen by some other dictionaries as a joke or "made up Word purely for the purpose of inventing the longest Word".

The meaning of this Word is "a lung disease caused by breathing volcanic dust".