v. analyze; examine; identify
How to diagnose a sick fish by their behavioral changes and what you can do to cure the illness.
Sentence in Classic:
Yet he did not repress all boyish playfulness, since he declared it to be as necessary as a rash to a doctor, inasmuch as it enabled him to diagnose what lay hidden within.
Dead Souls By Nikolai Vasilievich Gogol Context
Where it is ill, we probe; and the sickness once diagnosed, the study of the cause leads to the discovery of the remedy.
Les Misérables (V4) By Victor Hugo Context