a. The killing of one's brother or sister.
b. One who has killed one's brother or sister.
2. The accidental killing of an ally caused by a discharge of a military weapon.
[Middle English, from Old French, from Latin frātricīdium and frātricīda : frāter, frātr-, brother; see bhrāter- in the Appendix of Indo-European roots + -cīdium and -cīda, -cide.]
frat′ri·cidal (-sīdl) adj.
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