Source : Webster's Revised Unabridged Dictionary (1913)

Etiology \E`ti*ol"o*gy\, n. [Cf. F. ['e]tiologie.]
   The science of causes. Same as ?{tiology}.

Source : WordNet®

etiology
     n 1: the cause of a disease [syn: {aetiology}]
     2: the philosophical study of causation [syn: {aetiology}]