The spelling of the word "Sermion" can be explained using IPA phonetic transcription. The word is pronounced as /ˈsɜːmɪən/. The first syllable is pronounced as "sir" with a long "e" sound, while the second syllable is pronounced as "me" with a short "i" sound. The "o" in the word is pronounced as a short "u" sound, and the final "n" is pronounced as a regular "n" sound. Therefore, the correct spelling of the word "Sermion" accurately reflects its pronunciation.