The spelling of the word "most adust" is quite unusual and can be tricky to decipher. The IPA phonetic transcription for this word is /moʊst əˈdʌst/. The word "most" is pronounced as it normally would be, with a long "o" sound and a soft "s" sound. However, the word "adust" is not commonly used and may not be familiar to many people. It means "burnt or scorched", and is pronounced with a short "a" sound and a hard "st" sound at the end.
The word "adust" stems from the Latin word "adustus", which means "burnt", "scorched", or "darkened by the sun". It ultimately traces back to the Latin verb "adūrere", which means "to burn" or "to scorch". The term "most adust" is a superlative form of "adust" and refers to something that is extremely burnt or darkened.