The Collaborative International Dictionary of English v.0.48:

Cosinage \Cos"in*age\ (k?s"'n-?j), n. [See Cousinage.] (Law)
   (a) Collateral relationship or kindred by blood;
       consanguinity. --Burrill.
   (b) A writ to recover possession of an estate in lands, when
       a stranger has entered, after the death of the
       grandfather's grandfather, or other distant collateral
       relation. --Blackstone.
       [1913 Webster]