diagnose, diagnosed 1. To determine or distinguish the nature of a problem or an illness through a diagnostic analysis. 2. To determine the identity of (a disease, illness, etc.) by a medical examination: 'The doctor diagnosed the illness as influenza.' 3. To ascertain the cause or nature of (a disorder, malfunction, problem, etc.) from the sympto... Found on http://www.wordinfo.info/words/index/info/view_unit/2764/3