The word "diapnotic" refers to something that has the power to induce sleep or calmness. The spelling of this word can be explained using the International Phonetic Alphabet (IPA) as /daɪəˈnɑːtɪk/. The first syllable is pronounced with the diphthong "ai" as in "eye," while the second syllable has a long "a" sound followed by a nasal "n." The final syllable is pronounced with the "tic" sound commonly used in medical terminology. Overall, the spelling of "diapnotic" accurately reflects its pronunciation.
Diapnoic.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.