Polyphagian is a rare word that means an avid eater or glutton. The word is spelled with the prefix 'poly-' which means many, and the root word 'phag', which means eating. The suffix '-ian' is added to denote a person who has a particular quality or characteristic. The correct phonetic transcription for 'polyphagian' is /pɑlɪˈfeɪdʒiən/, where each symbol represents a particular sound in the English language. Despite its rarity, polyphagian is a valid word that can be used to describe someone with a voracious appetite.