The spelling of the word "most castaway" is straightforward once you understand its phonetic transcription. In IPA, the word is spelled /moʊst kæstəweɪ/. The "o" sound is pronounced as a long "o" and the "a" sound is pronounced as a short "a." The "y" sound at the end is represented by the IPA symbol /weɪ/. Overall, the word means "the majority of those shipwrecked on an island" and is spelled just as it sounds with the correct utilization of IPA phonetics.