The Collaborative International Dictionary of English v.0.48:

Cognominal \Cog*nom"i*nal\, a.
   Of or pertaining to a cognomen; of the nature of a surname.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cognominal \Cog*nom"i*nal\, n.
   One bearing the same name; a namesake. [Obs.] --Sir T.
   Browne.
   [1913 Webster]