The Collaborative International Dictionary of English v.0.48:

Primogenitive \Pri`mo*gen"i*tive\, a. [See Primogeniture.]
   Of or pertaining to primogeniture. [R.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Primogenitive \Pri`mo*gen"i*tive\, n.
   Primogeniture. [Obs.]
   [1913 Webster]

         The primogenitive and due of birth.      --Shak.
   [1913 Webster]