The spelling of the word "most undergrown" is straightforward when using the International Phonetic Alphabet (IPA) transcription. The word is pronounced as /məʊst ʌndəɡrəʊn/. The "most" part is pronounced as a monophthongal vowel sound /məʊst/ and the "undergrown" part is pronounced with a schwa sound for the "u" in "under" and a long "o" sound for "grown" /ʌndəɡrəʊn/. This word is not commonly used in everyday language, but understanding its pronunciation can be helpful when encountering it.