What is the longest word in Harry Potter and the Philosopher's Stone?

The longest Word in "Harry Potter and the Philosopher's Stone" is "Invisibility," which appears in the context of the Invisibility Cloak. The book features a variety of unique and whimsical terms, but "Invisibility" stands out due to its length and significance within the story. Other lengthy Words include "Philosopher" and "Hogwarts," but "Invisibility" takes the top spot.