The Collaborative International Dictionary of English v.0.48:

Fratricide \Frat"ri*cide\, n. [L. fratricidium a brother's
   murder, fr. fratricida a brother's murderer; frater, fratris,
   brother + caedere to kill: cf. F. fratricide.]
   1. The act of one who murders or kills his own brother.
      [1913 Webster]

   2. [L. fratricida: cf. F. fratricide.] One who murders or
      kills his own brother.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fratricide
    n 1: a person who murders their brother or sister
    2: fire that injures or kills an ally [syn: friendly fire,
       fratricide]
    3: the murder of your sibling

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "fratricide":
   aborticide, fungicide, genocide, germicide, herbicide, homicide,
   infanticide, insecticide, matricide, microbicide, parricide,
   patricide, pesticide, regicide, rodenticide, sororicide, suicide,
   uxoricide, vermicide



Bouvier's Law Dictionary, Revised 6th Ed (1856):

FRATRICIDE, criminal law. He who kills his brother or sister. The crime of
such a person is also called fratricide.