The Collaborative International Dictionary of English v.0.48:

Cossic \Cos"sic\ (k?s"s?k), Cossical \Cos"sic*al\ (-s?-kal), a.
   [It. cossico. See 2d Coss.]
   Of or relating to algebra; as, cossic numbers, or the cossic
   art. [Obs.] "Art of numbers cossical." --Digges (1579).
   [1913 Webster]