1 [noncount] : the act of identifying a disease, illness, or problem by examining someone or something

• The unusual combination of symptoms made accurate diagnosis difficult.
• She is an expert in the diagnosis and treatment of eye diseases.

2 [count] : a statement or conclusion that describes the reason for a disease, illness, or problem

• The diagnosis was a mild concussion.
• His doctor made an initial diagnosis of pneumonia.
• The committee published its diagnosis of the problems affecting urban schools.