The Collaborative International Dictionary of English v.0.48:

Agnation \Ag*na"tion\, n. [L. agnatio: cf. F. agnation.]
   1. (Civil Law) Consanguinity by a line of males only, as
      distinguished from cognation. --Bouvier.
      [1913 Webster]

WordNet (r) 3.0 (2006):

agnation
    n 1: line of descent traced through the paternal side of the
         family [syn: patrilineage, agnation]