The word "dumb chum" is spelled exactly how it sounds. In IPA phonetic transcription, it would be written as /dʌm tʃʌm/. The word "dumb" is pronounced with a short "u" sound, represented by the symbol /ʌ/ in IPA. The "ch" in "chum" is pronounced as a voiceless postalveolar affricate, indicated by the symbol /tʃ/. Together, the two words create a rhyming phrase commonly used to refer to a foolish or naive friend.