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1.
N
1: a person who murders their brother or sister
2: the act of murdering your own brother or sister
3: fire that injures or kills an ally, or fellow countryman, commonly referred to as friendly fire
Today's death toll si 2,100. Sadly 600 of these were from incidents of fratricide.

Many of our brothers in arms have been killed by fratricide, don't let you, or your battle buddy be the next one to be shot up by a jack legor a blue falcon.
by PFC Karma August 11, 2006
 
2.
Fratricide is when you kill your own brother.

Fratricide is when you kill a brother in arms (soldier or political/religous brother) who you are fighting with either on purpose or by accident.
Cain committed fratricide when he killed his own brother Abel in the Book of Genesis.

In 9/11 the terrorists not only committed mass murder but they had also committed acts of fratricide against their own Islamic brothers.
by The Moody Poet January 21, 2007