By Bocca Bre On Mar 24, 2021. The plural of diagnosis is diagnoses. The verb is to diagnose, and a person who diagnoses is called a diagnostician. misdiagnosis. noun. mis· di· ag· no· sis | (ˌ)mis-ˌdī-ig-ˈnō-səs plural misdiagnoses - ˌsēz « ,BizWritingTip response: “Diagnosis” is a singular word meaning the identification of an illness or disease

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