5 Longest Word In The World (In Letters) Rate this post 5 Longest Word In The World (In Letters) S. No. Word 1. Pneumonoultramicroscopicsilicovolcanoconiosis 2. Hippopotomonstrosesquippedaliophobia 3. Supercalifragilisticexpialidocious 4. Pseudopseudohypoparathyroidism 5. Floccinaucinihilipilification Source: Wikipedia Sharing Is Caring: