The correct spelling of the word "Achilleinum" can be confusing due to the presence of double consonants and a unique vowel sound. The word is pronounced as [uh-kil-ee-nuhm], with emphasis on the second syllable. The double consonants in the word clarify that both the "l" and "n" sounds should be pronounced distinctly, similar to the word "million." The vowel sound in the middle of the word is represented by the letters "ee," indicating a long "e" sound. With practice, remembering the spelling and pronunciation of "Achilleinum" will become easier.