Webster's Revised Unabridged Dictionary · 1913

aetiology

aetiology (ē`ti*ol"o*jy) , noun

[Latin aetologia, Greek a'itiologi`a; a'iti`a cause + lo`gos description: compare French étiologie.]

1.
The science, doctrine, or demonstration of causes; esp., the investigation of the causes of any disease; the science of the origin and development of things; etiology.
2.
The assignment of a cause.
3.
(Medicine) The cause or origin of a disease. Now more commonly written etiology.

Also: etiology