aetiology

The establishment of a cause, origin, or reason for something.

I do not know where the idea first arose of enlisting internal (subjective) excitations of the sensory organs as well as external sensory stimuli; but it is in fact done in all the more recent accounts of the aetiology of dreams [translating Traumätiologie].

The study of causes or causation.

The study or investigation of the causes of disease; a scientific explanation for the origin of a disease.

A cause of disease or of any particular case of a disease (but see pathology § Usage notes).