mid-15c., "person who kills a brother;" 1560s, "act of killing a brother," from Latin fratricida "brother-slayer," from frater "brother" (from PIE root *bhrater- "brother") + cida "killer;" in the later use from cidum "a killing," both from caedere "to kill, to cut down" (from PIE root *kae-id- "to strike"). Among several Old English words for this were broðorbana "one who kills a brother;" broðorcwealm "act of killing a brother."
-al 1
suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).