This is the 2981st most frequent Russian word.
диагнозом
The Russian word "диагнозом" means "diagnosis" (instrumental case).
The word 'диагнозом' here expresses the instrumental case, referring to the tool or means by which something is achieved, i.e., an accurate diagnosis.
Этот врач известен своим точным диагнозом.
This doctor is known for their accurate diagnosis.
In this sentence, 'диагнозом' again represents the instrumental case, used to describe the means of surprise — an unexpected diagnosis.
Он удивил нас своим неожиданным диагнозом.
He surprised us with his unexpected diagnosis.
Here, 'диагнозом' indicates the method or means ('a correct diagnosis') by which the identification of the illness was achieved.