Cata \Cat"a\ [Gr. kata`.]
The Latin and English form of a Greek preposition, used as a
prefix to signify down, downward, under, against, contrary or
opposed to, wholly, completely; as in cataclysm, catarrh. It
sometimes drops the final vowel, as in catoptric; and is
sometimes changed to cath, as in cathartic, catholic.
[1913 Webster]