The Collaborative International Dictionary of English v.0.48:

Fraternal \Fra*ter"nal\, a.[F. fraternel, LL. fraternalis, fr.
   L. fraternus, fr. frater brother. See Brother.]
   Of, pertaining to, or involving, brethren; becoming to
   brothers; brotherly; as, fraternal affection; a fraternal
   embrace. -- Fra*ter"nal*ly, adv.
   [1913 Webster]

         An abhorred, a cursed, a fraternal war.  --Milton.
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         Fraternal love and friendship.           --Addison.
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WordNet (r) 3.0 (2006):

fraternally
    adv 1: in a brotherly manner