Etiology (alternately aetiology, aitiology)
is the study of causation. The term (deriving from the Greek
words aitia = cause and logos = word/speech) is used in philosophy,
physics and biology in reference to the causes of various phenomena.
It is generally the study of why things occur, or even the reasons
behind the way that things act.
In medicine in particular, the term means the
occurrences, reasons, and variables of diseases or pathologies.
On  there is a informative text about the etiology of cleft
lips explaining several methods of the etiological science.
An aetiological myth is a myth intended to
explain a name. For example, the name Delphoi and its associated
deity, Apollon Delphinios, are explained in the Homeric Hymn
which tells how Apollo carried Cretans over the sea in the shape
of a dolphin to make them his priests. While there is an actual
etymological connection between Delphoi and delphis (delphus
means "womb"), many aetiological myths are based on
popular etymology (the term "Amazon", for example).